Fractional redundant array of silicon independent elements

ABSTRACT

Higher-level redundancy information computation enables a Solid-State Disk (SSD) controller to provide higher-level redundancy capabilities to maintain reliable operation in a context of failures of non-volatile (e.g. flash) memory elements during operation of an SSD implemented in part by the controller. For example, a first computation is an XOR, and a second computation is a weighted-sum. Various amounts of storage are dedicated to storing the higher-level redundancy information, such as amounts equivalent to an integer multiple of flash die (e.g. one, two, or three entire flash die), and such as amounts equivalent to a fraction of a single flash die (e.g. one-half or one-fourth of a single flash die).

CROSS REFERENCE TO RELATED APPLICATIONS

Priority benefit claims for this application are made in theaccompanying Application Data Sheet, Request, or Transmittal (asappropriate, if any). To the extent permitted by the type of the instantapplication, this application incorporates by reference for all purposesthe following applications, all commonly owned with the instantapplication at the time the invention was made:

-   -   U.S. Provisional application (Docket No. SF-10-10 and Ser. No.        61/418,846), filed 12-01-2010, first named inventor Jeremy Isaac        Nathaniel WERNER, and entitled DYNAMIC HIGHER-LEVEL REDUNDANCY        MODE MANAGEMENT WITH INDEPENDENT SILICON ELEMENTS;    -   U.S. Provisional application (Docket No. SF-10-14 and Ser. No.        61/433,918), filed 01-18-2011, first named inventor Jeremy Isaac        Nathaniel WERNER, and entitled HIGHER-LEVEL REDUNDANCY        INFORMATION COMPUTATION;    -   PCT Application (Docket No. SF-10-10PCT and Serial No.        PCT/US11/062726), filed Nov. 30, 2011, first named inventor        Jeremy Isaac Nathaniel WERNER, and entitled DYNAMIC HIGHER-LEVEL        REDUNDANCY MODE MANAGEMENT WITH INDEPENDENT SILICON ELEMENTS;    -   PCT Application (Docket No. SF-10-14PCT and Serial No.        PCT/US12/21682), filed 01-18-2012, first named inventor Jeremy        Isaac Nathaniel WERNER, and entitled HIGHER-LEVEL REDUNDANCY        INFORMATION COMPUTATION; and    -   U.S. Provisional application (Docket No. L12-1959US1 and Ser.        No. 61/682,561), filed Aug. 13, 2012, first named inventor        Earl T. COHEN, and entitled FRACTIONAL REDUNDANT ARRAY OF        SILICON INDEPENDENT ELEMENTS.

BACKGROUND Field

Advancements in storage technology and manufacturing are needed toprovide improvements in cost, profitability, performance, efficiency,and utility of use.

Related Art

Unless expressly identified as being publicly or well known, mentionherein of techniques and concepts, including for context, definitions,or comparison purposes, should not be construed as an admission thatsuch techniques and concepts are previously publicly known or otherwisepart of the prior art. All references cited herein (if any), includingpatents, patent applications, and publications, are hereby incorporatedby reference in their entireties, whether specifically incorporated ornot, for all purposes.

Synopsis

The invention may be implemented in numerous ways. e.g., as a process,an article of manufacture, an apparatus, a system, a composition ofmatter, and a computer readable medium such as a computer readablestorage medium (e.g., media in an optical and/or magnetic mass storagedevice such as a disk, an integrated circuit having non-volatile storagesuch as flash storage), or a computer network wherein programinstructions are sent over optical or electronic communication links.The Detailed Description provides an exposition of one or moreembodiments of the invention that enable improvements in cost,profitability, performance, efficiency, and utility of use in the fieldidentified above. The Detailed Description includes an Introduction tofacilitate understanding of the remainder of the Detailed Description.The Introduction includes Example Embodiments of one or more of systems,methods, articles of manufacture, and computer readable media inaccordance with concepts described herein. As is discussed in moredetail in the Conclusions, the invention encompasses all possiblemodifications and variations within the scope of the issued claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates selected details of an embodiment of a Solid-StateDisk (SSD) including an SSD controller providing fractional higher-levelredundancy for Non-Volatile Memories (NVMs).

FIG. 1B illustrates selected details of various embodiments of systemsincluding one or more instances of the SSD of FIG. 1A.

FIG. 2 illustrates selected details of an embodiment of mapping aLogical Page Number (LPN) portion of a Logical Block Address (LBA).

FIG. 3 illustrates selected details of an embodiment of accessing aNon-Volatile Memory (NVM) at a read unit address to produce read dataorganized as various read units, collectively having a length measuredin quanta of read units.

FIG. 4A illustrates selected details of an embodiment of a read unit.

FIG. 4B illustrates selected details of another embodiment of a readunit.

FIG. 5 illustrates selected details of an embodiment of a header havinga number of fields.

FIG. 6 illustrates selected details of an embodiment of blocks, pages,and read units of multiple NVM devices (e.g. one or more flash dieand/or flash chips) managed in logical slices and/or sections.

FIG. 7 illustrates selected details of various embodiments ofhigher-level redundancy techniques.

FIG. 8 illustrates selected details of an embodiment of dynamichigher-level redundancy mode management with a Redundant Array ofSilicon Independent Elements (RASIE).

FIG. 9 illustrates an embodiment of read units having lower-levelredundancy information of adaptive code rates protected by higher-levelredundancy information stored in one or more of the read units.

FIG. 10 illustrates selected details of an embodiment of higher-levelredundancy information result and data source correspondences.

FIG. 11 illustrates selected details of an embodiment of higher-levelredundancy information computations.

FIG. 12 illustrates selected details of an embodiment of recovery fromone (lower-level) failure (during a single operation).

FIGS. 13A-13D illustrate selected details of an embodiment of recoveryfrom two (lower-level) failures (during a single operation).

FIGS. 14A and 14B illustrate selected details of an embodiment ofcomputing higher-level redundancy information with respect to pagesreceived from NVMs.

FIGS. 15A-15C illustrate selected details of an embodiment of backingout of a computation of higher-level redundancy information with respectto a write provided to NVMs.

FIGS. 16A-16C illustrate selected details of an embodiment of fractionalhigher-level redundancy.

LIST OF REFERENCE SYMBOLS IN DRAWINGS

Ref. Symbol Element Name  100 SSD Controller  101 SSD  102 Host  103(optional) Switch/Fabric/Intermediate Controller  104 IntermediateInterfaces  105 OS  106 FirmWare (FW)  107 Driver  107D dotted-arrow(Host Software ←→ I/O Device Communication)  109 Application  109Ddotted-arrow (Application ←→ I/O Device Communication via driver)  109Vdotted-arrow (Application ←→ I/O Device Communication via VF)  110External Interfaces  111 Host Interfaces  112C (optional) Card Memory 113 Tag Tracking  114 Multi-Device Management Software  115 HostSoftware  116 I/O Card  117 I/O & Storage Devices/Resources  118 Servers 119 LAN/WAN  121 Data Processing  123 Engines  131 Buffer  133 DMA  135ECC-X  137 Memory  141 Map  143 Table  151 Recycler  161 ECC  171 CPU 172 CPU Core  173 Command Management  175 Buffer Management  177Translation Management  179 Coherency Management  180 Memory Interface 181 Device Management  182 Identity Management  190 Device Interfaces 191 Device Interface Logic  192 Flash Device  193 Scheduling  194 FlashDie  199 NVM  211 LBA  213 LPN  215 Logical Offset  221 Map Info for LPN 223 Read Unit Address  225 Length in Read Units  311 Read Data  313First Read Unit  315 Last Read Unit  401A Read Unit  401B Read Unit 410B Header Marker (HM)  411A Header 1  411B Header 1  412B Header 2 419A Header N  419B Header N  421A Data Bytes  421B Data Bytes  422BData Bytes  429B Data Bytes  431A Optional Padding Bytes  431B OptionalPadding Bytes  501 Header  511 Type  513 Last Indicator  515 Flags  517LPN  519 Length  521 Offset  600 Striping Direction  610.0, 610.1, FlashDie  610.61,  610.62,  610.63,  610.64,  610.65  610.0B0, Blocks 610.0B1,  610.0B2,  610.0BB,  610.1B0,  610.1B1,  610.1B2,  610.1BB, 610.63B0,  610.63B1,  610.63B2,  610.63BB,  610.64B0,  610.64B1, 610.64B2,  610.64BB,  610.65B0,  610.65B1,  610.65B2,  610.65BB 610.0P0, Pages  610.0P1,  610.0P2,  610.0PP,  610.63P0,  610.63P1, 610.63P2,  610.63PP,  610.64P0,  610.64P1,  610.64P2,  610.64PP, 610.65P0,  610.65P1,  610.65P2,  610.65PP  610.0R0, Read Units (RUs) 610.0R1,  610.0RR,  610.1R0,  610.1R1,  610.1RR,  610.65R0,  610.65R1, 610.65RR  660.0, 660.1, R-blocks  660.2, 660.R  720 Flash Device(s) 730 Interface Channel(s)  740 Extra Flash Device(s)  750 ExtraInterface Channel(s)  801 Start  802 Operate in First Higher-LevelRedundancy Mode  803 Failure?  804 Reduce Free Space  805 Rearrange DataStorage  806 Recover/Store Failed User Data  807 Determine/Store RevisedHigher-Level Redundancy Information  808 Operate in Second Higher-LevelRedundancy Mode  809 Dynamically Transition Operating Mode  899 End 911, 931, 951, Read Unit  971  911.E, 931.E, Lower-Level ECC  951.E,971.E  911.U, 931.U, User Data  951.U, 971.0 1001 Result 1002 Result1003 Result 1010 R0 1011 R1 1019 Data 1401A Start 1401B Start 1402AIssue Read Operation 1402B Page Ready? 1403A All Issued? 1403B PerformPage-Based Computations 1404B Pages Finished? 1499A End 1499B End 1501AStart 1501B Start 1502A Issue Write Operation 1502B Write OK? 1503A AllIssued? 1503B Backout Write from Redundancy 1504B Writes Finished? 1599AEnd 1599B End 1600, 1601, R-pages 1602, 1609 1600.D, Data Information1601.D, 1602.D, 1609.D, 1610.D, 1620.D, 1690.D 1600.R, RedundancyInformation 1601.R, 1602.R, 1609.R, 1610.R, 1620.R, 1690.R 1700Concurrently Operate in First and Second Granularity Higher-LevelRedundancy Modes 1701 Start 1702 Operate in First GranularityHigher-Level Redundancy Mode 1703 Read/Write According to FirstGranularity Higher-Level Redundancy Mode 1704 Operate in SecondGranularity Higher-Level Redundancy Mode 1705 Read/Write According toSecond Granularity Higher-Level Redundancy Mode 1706 Granularity? 1706.1First 1706.2 Second 1707 Read/Write Request

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures illustrating selecteddetails of the invention. The invention is described in connection withthe embodiments. The embodiments herein are understood to be merelyexemplary, the invention is expressly not limited to or by any or all ofthe embodiments herein, and the invention encompasses numerousalternatives, modifications, and equivalents. To avoid monotony in theexposition, a variety of word labels (such as: first, last, certain,various, further, other, particular, select, some, and notable) may beapplied to separate sets of embodiments; as used herein such labels areexpressly not meant to convey quality, or any form of preference orprejudice, but merely to conveniently distinguish among the separatesets. The order of some operations of disclosed processes is alterablewithin the scope of the invention. Wherever multiple embodiments serveto describe variations in process, system, and/or program instructionfeatures, other embodiments are contemplated that in accordance with apredetermined or a dynamically determined criterion perform staticand/or dynamic selection of one of a plurality of modes of operationcorresponding respectively to a plurality of the multiple embodiments.Numerous specific details are set forth in the following description toprovide a thorough understanding of the invention. The details areprovided for the purpose of example and the invention may be practicedaccording to the claims without some or all of the details. For thepurpose of clarity, technical material that is known in the technicalfields related to the invention has not been described in detail so thatthe invention is not unnecessarily obscured.

INTRODUCTION

This introduction is included only to facilitate the more rapidunderstanding of the Detailed Description; the invention is not limitedto the concepts presented in the introduction (including explicitexamples, if any), as the paragraphs of any introduction are necessarilyan abridged view of the entire subject and are not meant to be anexhaustive or restrictive description. For example, the introductionthat follows provides overview information limited by space andorganization to only certain embodiments. There are many otherembodiments, including those to which claims will ultimately be drawn,discussed throughout the balance of the specification.

Acronyms

At least some of the various shorthand abbreviations (e.g. acronyms)defined here refer to certain elements used herein.

Acronym Description AHCI Advanced Host Controller Interface APIApplication Program Interface ATA Advanced Technology Attachment (ATAttachment) BCH Bose Chaudhuri Hocquenghem CD Compact Disk CF CompactFlash CMOS Complementary Metal Oxide Semiconductor CPU CentralProcessing Unit CRC Cyclic Redundancy Check DAS Direct Attached StorageDDR Double-Data-Rate DMA Direct Memory Access DNA Direct NAND AccessDRAM Dynamic Random Access Memory DVD Digital Versatile/Video Disk DVRDigital Video Recorder ECC Error-Correcting Code eMMC embeddedMultiMediaCard eSATA external Serial Advanced Technology Attachment GPSGlobal Positioning System HDD Hard Disk Drive I/O Input/Output ICIntegrated Circuit IDE Integrated Drive Electronics JPEG JointPhotographic Experts Group LAN Local Area Network LBA Logical BlockAddress LDPC Low-Density Parity-Check LPN Logical Page Number MLCMulti-Level Cell MMC MultiMediaCard MPEG Moving Picture Experts GroupNAS Network Attached Storage NCQ Native Command Queuing NVM Non-VolatileMemory ONA Optimized NAND Access ONFI Open NAND Flash Interface OSOperating System PC Personal Computer PCIe Peripheral ComponentInterconnect express (PCI express) PDA Personal Digital Assistant PHYPHYsical interface POS Point Of Sale RAID Redundant Array ofInexpensive/Independent Disks RASIE Redundant Array of SiliconIndependent Elements ReRAM Resistive Random Access Memory RSReed-Solomon SAN Storage Attached Network SAS Serial Attached SmallComputer System Interface (Serial SCSI) SATA Serial Advanced TechnologyAttachment (Serial ATA) SCSI Small Computer System Interface SD SecureDigital SDR Single-Data-Rate SLC Single-Level Cell SMART Self-MonitoringAnalysis and Reporting Technology SRAM Static Random Access Memory SSDSolid-State Disk/Drive UFS Unified Flash Storage USB Universal SerialBus VF Virtual Function WAN Wide Area Network

NAND flash memory uses an array of floating gate transistors to storeinformation. In SLC technology, each bit cell (e.g. floating gatetransistor) is enabled to store one bit of information. In MLCtechnology, each bit cell is enabled to store multiple bits ofinformation. As manufacturing technology (e.g. CMOS technology) scalesdown, each floating gate stores fewer electrons. Further, as storagecapacity and density increase, each bit cell stores more bits.Therefore, values stored in the bit cells are represented by smallervoltage ranges. Uncertainties in sensing and/or changes in amount ofstored electrons over time increase a probability for data to be storedor read incorrectly. Use of one or more redundancy and/or ECC techniques(e.g. at a lower-level) enables correct retrieval of otherwise corrupteddata from NAND flash memory, overcoming, in some usage scenarios, someof the aforementioned difficulties.

Some types of SSDs use flash memory to provide non-volatile storage(e.g., the flash memory retains information without application ofpower). Use of one or more ECC and/or redundancy techniques (e.g. at ahigher-level) enables correct retrieval of otherwise corrupted data fromflash memory, and/or enables proper system-level operation of an SSDeven when one or more flash memory elements fail intermittently orpermanently.

For example, an SSD controller enables dynamic higher-level redundancymode management with independent silicon elements to provide gracefuldegradation as one or more NVM (e.g. flash) elements fail duringoperation of an SSD implemented in part by the controller. A portion ofthe NVM is read. If an error occurs that is not correctable usinglower-level redundancy and/or error correction (such as in accordancewith one or more ECC techniques), then higher-level redundancy and/orerror correction (such as in accordance with one or more RASIEtechniques and/or dynamic higher-level redundancy mode managementtechniques) is used to attempt to correct the error. If a failure of oneof the NVM elements is detected by the lower-level and/or thehigher-level redundancy and/or error correction, and/or by othertechniques (such as a failing status reported by one or more of the NVMelements), then the higher-level redundancy and/or error correction isdynamically transitioned from operating in a current mode to operatingin a new mode. The transition includes one or more of reducing freespace available on the SSD, rearranging data storage of the SSD,recovering/storing failed user data (if possible), anddetermining/storing revised higher-level redundancy and/or errorcorrection information. Operation then continues in the new mode. Ifanother failure of another one of the NVM elements is detected with thehigher-level redundancy and/or error correction now operating in the newmode, then another transition is made to another higher-level redundancyand/or error correction mode. Writing the NVM is in accordance with ahigher-level redundancy and/or error correction operating mode,including determining/storing higher-level redundancy and/or errorcorrection information in accordance with the higher-level redundancyand/or error correction operating mode and write data.

If greater than a threshold number and/or rate of lower-level errorcorrections and/or one or more failures occur for an area of memory,then optionally the area of memory is dynamically transitioned tooperating in a new higher-level redundancy and/or error correctionoperating mode that is enabled to recover from more errors than acurrent higher-level redundancy and/or error correction operating mode.For example, if the current higher-level redundancy and/or errorcorrection operating mode is none (e.g. no higher-level redundancyinformation is computed and/or used to recover from a failure oflower-level redundancy to correct an error), then the new higher-levelredundancy and/or error correction operating mode is one that enablesrecovery from a single failure that is uncorrectable by the lower-levelredundancy. For another example, if the current higher-level redundancyand/or error correction operating mode is one that enables recovery froma single failure that is uncorrectable by the lower-level redundancy,then the new higher-level redundancy and/or error correction operatingmode is one that enables recovery from two failures that areuncorrectable by the lower-level redundancy.

Determining/storing higher-level redundancy and/or error correctioninformation is in accordance, in some embodiments and/or usagescenarios, with computation of higher-level redundancy information.Higher-level redundancy information computation enables an SSDcontroller to provide higher-level redundancy capabilities to maintainreliable operation in a context of failures of non-volatile (e.g. flash)memory elements during operation of an SSD implemented in part by thecontroller. A first portion of higher-level redundancy information iscomputed using parity coding via an XOR of all pages in a portion ofdata (e.g. a stripe) to be protected by the higher-level redundancyinformation. A second portion of the higher-level redundancy informationis computed using a weighted-sum technique, each page in the portionbeing assigned a unique non-zero “index” as a weight when computing theweighted-sum. Arithmetic is performed over a finite field (such as aGalois Field, or such as the integers mod p where p is a prime).

The portions of the higher-level redundancy information are computablein any order, such as an order determined by an order of completion ofone or more read operations performed on NVM elements, or such as anorder based on order of data returned and/or available from NVMelements, enabling, in various embodiments, reduced or eliminatedbuffering. The any order computability enables, in various embodiments,computing recovery data values and/or backing out of a write usingrelatively little temporary and/or intermediate buffering and/or state.The portions of the higher-level redundancy information are computablewith any degree of parallelism, such as determined by availablededicated hardware elements, enabling, in various embodiments, reducedlatency processing and/or reduced memory (e.g. NVM) bandwidth usage.

In some embodiments, one or more entire NVM elements (e.g. flash die)are dedicated to higher-level redundancy information, such as forvarious so-called “non-fractional” RASIE techniques. In some situations,customers of storage systems prefer storage capabilities at variousso-called “binary capacity” points (for example 256 GB and 128 GB), anddedicating an entire NVM element or a plurality of entire NVM elementsto error recovery results in burdensome increased costs. In someembodiments and/or usage scenarios, so-called “fractional” RASIEtechniques reduce higher-level redundancy information overhead to lessthan one entire NVM element. The fractional higher-level redundancytechniques enable RASIE benefits for lower capacity points whileretaining binary capacity. In some embodiments, fractional higher-levelredundancy techniques include striping data across multiple blocks ofNVM elements.

Example Embodiments

In concluding the introduction to the detailed description, what followsis a collection of example embodiments, including at least someexplicitly enumerated as “ECs” (Example Combinations), providingadditional description of a variety of embodiment types in accordancewith the concepts described herein; these examples are not meant to bemutually exclusive, exhaustive, or restrictive; and the invention is notlimited to these example embodiments but rather encompasses all possiblemodifications and variations within the scope of the issued claims andtheir equivalents.

EC1) A method comprising:

-   -   writing a respective page to each of a respective first block of        a plurality of non-volatile memory devices;    -   writing a respective page to each of a respective second block        of the plurality of non-volatile memory devices, the respective        second block different from the respective first block; and    -   wherein one or more of the respective pages contains redundancy        of an erasure-correcting code protecting all of the respective        pages.

EC2) The method of EC1, wherein a fraction of the respective pagescontaining the redundancy of the erasure-correcting code is less than 1in a number of the plurality of non-volatile memory devices.

EC3) The method of EC2, wherein the fraction is 1 in an integer multipleof the number of the plurality of non-volatile memory devices.

EC4) The method of EC3, wherein the integer multiple is a power of two.

EC5) The method of EC1, wherein the erasure-correcting code is anerror-correcting code.

EC6) The method of EC1, wherein the respective first blocks aredual-plane blocks.

EC7) A system comprising:

-   -   a plurality of non-volatile memory devices, each of the        non-volatile memory devices comprising a plurality of blocks,        each of the blocks comprising a plurality of pages;    -   an erasure-correcting code generator operable to generate one or        more pages of redundant data protecting a respective plurality        of pages of user data, the one or more pages of redundant data        and the respective plurality of pages of user data forming a        codeword of an erasure-correcting code;    -   wherein the one or more pages of redundant data and the        respective plurality of pages of user data are each enabled to        be stored into a separate respective one of the pages of at        least some of the blocks such that more than one of the        non-volatile memory devices contains more than one of the one or        more pages of redundant data and the respective plurality of        pages of user data, and such that none of the at least some of        the blocks contains more than one of the one or more pages of        redundant data and the respective plurality of pages of user        data; and    -   whereby a failure of at least one of the at least some of the        blocks is correctable by the erasure-correcting code.

EC8) The system of EC7, wherein a number of the one or more pages ofredundant data is equal to a number of the at least one of the at leastsome of the blocks that is correctable.

EC9) The system of EC7, further comprising an erasure-correcting codecorrector enabled to process information read from at least some of theseparate respective ones of the pages of the at least some of the blocksto correct others of the separate respective ones of the pages of the atleast some of the blocks.

EC10) The system of EC7, further comprising an error-correcting codegenerator enabled to encode each of the one or more pages of redundantdata and the respective plurality of pages of user data to producerespective error-correcting information, the respective error-correctinginformation enabled to be stored into the separate respective ones ofthe pages of the at least some of the blocks along with thecorresponding one or more pages of redundant data and the respectiveplurality of pages of user data.

EC11) A system comprising:

-   -   a means for computing one or more units of higher-level        redundancy information based at least in part on a plurality of        units of data storage information; and    -   wherein the means for computing comprises a means for        accumulating a weighted sum of a respective non-zero unique        constant value for each of the units of data storage information        multiplied by contents of the units of data storage information        as at least a portion of the units of higher-level redundancy        information.

EC12) The system of EC11, further comprising a means for storing theunits of higher-level redundancy information and the units of datastorage information in portions of one or more non-volatile memorydevices.

EC13) The system of EC12, wherein the portions comprise one or moreintegral numbers of pages of the non-volatile memory devices, and thenon-volatile memory devices comprise one or more flash memories.

EC14) The system of EC11, wherein the units correspond to one or moreintegral numbers of pages of one or more flash memories.

EC15) The system of EC11, wherein the units of higher-level redundancyinformation are not computable as a remainder of a polynomial divisionby a generator polynomial of corresponding bytes of the units of datastorage information.

EC16) The system of EC11, wherein the means for accumulating is enabledto accumulate at least a portion of the weighted sum incrementally.

EC17) The system of EC16, wherein the means for accumulating is furtherenabled to process more than one of the units of data storageinformation in parallel.

EC18) The system of EC17, wherein the more than one of the unitscorrespond to one or more integral numbers of pages of one or more flashmemories.

EC19) The system of EC11, wherein the means for accumulating is enabledto accumulate at least a portion of the weighted sum in an orderingcorresponding to an ordering of read operation completion by one or moreflash memories.

EC20) The system of EC11, wherein the means for accumulating is enabledto accumulate at least a portion of the weighted sum in an orderingcorresponding to an ordering of data returned from one or more flashmemories.

EC21) The system of EC20, wherein the ordering of data returned is basedat least in part on an order that data is available from the one or moreflash memories.

EC22) The system of EC11, wherein the means for accumulating is enabledto accumulate at least a portion of the weighted sum in parallel.

EC23) The system of EC11, wherein the means for accumulating is enabledto accumulate at least a portion of the weighted sum in parallel, theportion corresponding to elements of the units of data storageinformation that are retrievable from corresponding pages of one or moreflash memories.

EC24) The system of EC23, wherein the elements are determined, at leastin part, by an order of completion of read operations of thecorresponding pages.

EC25) The system of EC12, further comprising a means for determining ifone or more of the portions have a lower-level error correction failurewhen read.

EC26) The system of EC12, further comprising a means for reading one ormore of the portions.

EC27) The system of EC11, wherein the means for accumulating a weightedsum is enabled to selectively exclude from the weighted sum up to two ofthe units of data storage information.

EC28) The system of EC27, further comprising means for processingresults of the means for accumulating to restore the excluded units ofthe data storage information.

EC29) The system of EC27, wherein the means for accumulating is enabledto accumulate at least a portion of the weighted sum incrementally andin an ordering corresponding to an ordering of read operation completionby one or more non-volatile memory devices.

EC30) The system of EC27, wherein the means for accumulating is enabledto accumulate at least a portion of the weighted sum incrementally andin an ordering corresponding to an ordering of data returned from one ormore non-volatile memory devices.

EC31) The system of EC30, wherein the ordering of data returned is basedat least in part on an order that data is available from the one or morenon-volatile memory devices.

EC32) The system of EC11, wherein the units of higher-level redundancyinformation and the units of data storage information correspond torespective pages of one or more flash memories.

EC33) The system of EC32, wherein the flash memories are comprised of aplurality of die, and each of the respective pages are on a unique oneof the die.

EC34) The system of EC11, further comprising a means for storing theunits of higher-level redundancy information and the units of datastorage information in portions of one or more flash memories at leastin part in response to requests from a computing host.

EC35) The system of EC34, further comprising a means for interfacing therequests with the computing host.

EC36) The system of EC35, wherein the means for interfacing the requestswith the computing host is compatible with a storage interface standard.

EC37) The system of EC34, wherein the means for storing comprises ameans for interfacing with the flash memories.

EC38) The system of EC37, wherein the means for interfacing with theflash memories comprises a flash memory interface.

EC39) The system of EC34, further comprising:

-   -   a means for interfacing the requests with the computing host;        and    -   wherein the means for storing comprises a means for interfacing        with the flash memories.

EC40) The system of EC39, wherein the means are collectively implementedin a single Integrated Circuit (IC).

EC41) The system of EC39, wherein the means are comprised in aSolid-State Disk (SSD).

EC42) The system of EC34, further comprising all or any portions of thecomputing host.

EC43) The system of EC13, further comprising at least one of the flashmemories.

EC44) A method comprising:

-   -   computing one or more units of higher-level redundancy        information based at least in part on a plurality of units of        data storage information; and    -   wherein the computing comprises accumulating a weighted sum of a        respective non-zero unique constant value for each of the units        of data storage information multiplied by contents of the units        of data storage information as at least a portion of the units        of higher-level redundancy information.

EC45) The method of EC44, further comprising storing the units ofhigher-level redundancy information and the units of data storageinformation in portions of one or more non-volatile memory devices.

EC46) The method of EC45, wherein the portions comprise one or moreintegral numbers of pages of the non-volatile memory devices, and thenon-volatile memory devices comprise one or more flash memories.

EC47) The method of EC44, wherein the units correspond to one or moreintegral numbers of pages of one or more flash memories.

EC48) The method of EC44, wherein the units of higher-level redundancyinformation are not computable as a remainder of a polynomial divisionby a generator polynomial of corresponding bytes of the units of datastorage information.

EC49) The method of EC44, wherein the accumulating comprisesaccumulating at least a portion of the weighted sum incrementally.

EC50) The method of EC49, wherein the accumulating further comprisesprocessing more than one of the units of data storage information inparallel.

EC51) The method of EC50, wherein the more than one of the unitscorrespond to one or more integral numbers of pages of one or more flashmemories.

EC52) The method of EC44, wherein the accumulating comprisesaccumulating at least a portion of the weighted sum in an orderingcorresponding to an ordering of read operation completion by one or moreflash memories.

EC53) The method of EC44, wherein the accumulating comprisesaccumulating at least a portion of the weighted sum in an orderingcorresponding to an ordering of data returned from one or more flashmemories.

EC54) The method of EC53, wherein the ordering of data returned is basedat least in part on an order that data is available from the one or moreflash memories.

EC55) The method of EC44, wherein the accumulating comprisesaccumulating at least a portion of the weighted sum in parallel.

EC56) The method of EC44, wherein the accumulating comprisesaccumulating at least a portion of the weighted sum in parallel, theportion corresponding to elements of the units of data storageinformation that are retrievable from corresponding pages of one or moreflash memories.

EC57) The method of EC56, wherein the elements are determined, at leastin part, by an order of completion of read operations of thecorresponding pages.

EC58) The method of EC45, further comprising determining if one or moreof the portions have a lower-level error correction failure when read.

EC59) The method of EC45, further comprising reading one or more of theportions.

EC60) The method of EC44, wherein the accumulating a weighted sum isselectively excludes from the weighted sum up to two of the units ofdata storage information.

EC61) The method of EC60, further comprising processing results of theaccumulating to restore the excluded units of the data storageinformation.

EC62) The method of EC60, wherein the accumulating comprisesaccumulating at least a portion of the weighted sum incrementally and inan ordering corresponding to an ordering of read operation completion byone or more non-volatile memory devices.

EC63) The method of EC60, wherein the accumulating comprisesaccumulating at least a portion of the weighted sum incrementally and inan ordering corresponding to an ordering of data returned from one ormore non-volatile memory devices.

EC64) The method of EC63, wherein the ordering of data returned is basedat least in part on an order that data is available from the one or morenon-volatile memory devices.

EC65) The method of EC44, wherein the units of higher-level redundancyinformation and the units of data storage information correspond torespective pages of one or more flash memories.

EC66) The method of EC65, wherein the flash memories are comprised of aplurality of die, and each of the respective pages are on a unique oneof the die.

EC67) The method of EC44, further comprising storing the units ofhigher-level redundancy information and the units of data storageinformation in portions of one or more flash memories at least in partin response to requests from a computing host.

EC68) The method of EC67, further comprising interfacing the requestswith the computing host.

EC69) The method of EC68, wherein the interfacing the requests with thecomputing host is compatible with a storage interface standard.

EC70) The method of EC67, wherein the storing comprises interfacing withthe flash memories.

EC71) The method of EC70, wherein the interfacing with the flashmemories comprises a flash memory interface.

EC72) The method of EC67, further comprising:

-   -   interfacing the requests with the computing host at least in        part via computing host interface logic circuitry; and    -   wherein the storing is at least in part via flash memory        interface logic circuitry enabled to interface with the flash        memories.

EC73) The method of EC72, wherein the computing host interface logiccircuitry and the flash memory interface logic circuitry arecollectively implemented in a single Integrated Circuit (IC).

EC74) The method of EC72, wherein the computing host interface logiccircuitry and the flash memory interface logic circuitry are comprisedin a Solid-State Disk (SSD).

EC75) The method of EC67, further comprising operating all or anyportions of the computing host.

EC76) The method of EC46, further comprising operating at least one ofthe flash memories.

EC77) A system comprising:

-   -   computing logic circuitry enabled to compute one or more units        of higher-level redundancy information based at least in part on        a plurality of units of data storage information; and    -   wherein the computing logic circuitry comprises accumulating        logic circuitry enabled to accumulate a weighted sum of a        respective non-zero unique constant value for each of the units        of data storage information multiplied by contents of the units        of data storage information as at least a portion of the units        of higher-level redundancy information.

EC78) The system of EC77, further comprising logic circuitry enabled tostore the units of higher-level redundancy information and the units ofdata storage information in portions of one or more non-volatile memorydevices.

EC79) The system of EC78, wherein the portions comprise one or moreintegral numbers of pages of the non-volatile memory devices, and thenon-volatile memory devices comprise one or more flash memories.

EC80) The system of EC77, wherein the units correspond to one or moreintegral numbers of pages of one or more flash memories.

EC81) The system of EC77, wherein the units of higher-level redundancyinformation are not computable as a remainder of a polynomial divisionby a generator polynomial of corresponding bytes of the units of datastorage information.

EC82) The system of EC77, wherein the accumulating logic circuitry isfurther enabled to accumulate at least a portion of the weighted sumincrementally.

EC83) The system of EC82, wherein the accumulating logic circuitry isfurther enabled to process more than one of the units of data storageinformation in parallel.

EC84) The system of EC83, wherein the more than one of the unitscorrespond to one or more integral numbers of pages of one or more flashmemories.

EC85) The system of EC77, wherein the accumulating logic circuitry isfurther enabled to accumulate at least a portion of the weighted sum inan ordering corresponding to an ordering of read operation completion byone or more flash memories.

EC86) The system of EC77, wherein the accumulating logic circuitry isfurther enabled to accumulate at least a portion of the weighted sum inan ordering corresponding to an ordering of data returned from one ormore flash memories.

EC87) The system of EC86, wherein the ordering of data returned is basedat least in part on an order that data is available from the one or moreflash memories.

EC88) The system of EC77, wherein the accumulating logic circuitry isfurther enabled to accumulate at least a portion of the weighted sum inparallel.

EC89) The system of EC77, wherein the accumulating logic circuitry isfurther enabled to accumulate at least a portion of the weighted sum inparallel, the portion corresponding to elements of the units of datastorage information that are retrievable from corresponding pages of oneor more flash memories.

EC90) The system of EC89, wherein the elements are determined, at leastin part, by an order of completion of read operations of thecorresponding pages.

EC91) The system of EC78, further comprising logic circuitry enabled todetermine if one or more of the portions have a lower-level errorcorrection failure when read.

EC92) The system of EC78, further comprising logic circuitry enabled toread one or more of the portions.

EC93) The system of EC77, wherein the accumulating logic circuitry isfurther enabled to selectively exclude from the weighted sum up to twoof the units of data storage information.

EC94) The system of EC93, further comprising logic circuitry enabled toprocess results of the accumulating logic circuitry to restore theexcluded units of the data storage information.

EC95) The system of EC93, wherein the accumulating logic circuitry isfurther enabled to accumulate at least a portion of the weighted sumincrementally and in an ordering corresponding to an ordering of readoperation completion by one or more non-volatile memory devices.

EC96) The system of EC93, wherein the accumulating logic circuitry isfurther enabled to accumulate at least a portion of the weighted sumincrementally and in an ordering corresponding to an ordering of datareturned from one or more non-volatile memory devices.

EC97) The system of EC96, wherein the ordering of data returned is basedat least in part on an order that data is available from the one or morenon-volatile memory devices.

EC98) The system of EC77, wherein the units of higher-level redundancyinformation and the units of data storage information correspond torespective pages of one or more flash memories.

EC99) The system of EC98, wherein the flash memories are comprised of aplurality of die, and each of the respective pages are on a unique oneof the die.

EC100) The system of EC77, further comprising flash storage logiccircuitry enabled to store the units of higher-level redundancyinformation and the units of data storage information in portions of oneor more flash memories at least in part in response to requests from acomputing host.

EC101) The system of EC100, further comprising computing host interfacelogic circuitry enabled to interface the requests with the computinghost.

EC102) The system of EC101, wherein the computing host interface logiccircuitry is compatible with a storage interface standard.

EC103) The system of EC100, wherein the flash storage logic circuitrycomprises flash memory interface logic circuitry enabled to interfacewith the flash memories.

EC104) The system of EC103, wherein the flash memory interface logiccircuitry comprises a flash memory interface.

EC105) The system of EC100, further comprising:

-   -   computing host interface logic circuitry enabled to interface        the requests with the computing host; and    -   wherein the flash storage logic circuitry comprises flash memory        interface logic circuitry enabled to interface with the flash        memories.

EC106) The system of EC105, wherein the computing host interface logiccircuitry and the flash memory interface logic circuitry arecollectively implemented in a single Integrated Circuit (IC).

EC107) The system of EC105, wherein the computing host interface logiccircuitry and the flash memory interface logic circuitry are comprisedin a Solid-State Disk (SSD).

EC108) The system of EC100, further comprising all or any portions ofthe computing host.

EC109) The system of EC79, further comprising at least one of the flashmemories.

EC110) A tangible computer readable medium having a set of instructionsstored therein that when executed by a processing element cause theprocessing element to perform operations comprising:

-   -   managing computing one or more units of higher-level redundancy        information based at least in part on a plurality of units of        data storage information; and    -   wherein the computing comprises accumulating a weighted sum of a        respective non-zero unique constant value for each of the units        of data storage information multiplied by contents of the units        of data storage information as at least a portion of the units        of higher-level redundancy information.

EC111) The tangible computer readable medium of EC110, wherein theoperations further comprise managing storing the units of higher-levelredundancy information and the units of data storage information inportions of one or more non-volatile memory devices.

EC112) The tangible computer readable medium of EC111, wherein theportions comprise one or more integral numbers of pages of thenon-volatile memory devices, and the non-volatile memory devicescomprise one or more flash memories.

EC113) The tangible computer readable medium of EC110, wherein the unitscorrespond to one or more integral numbers of pages of one or more flashmemories.

EC114) The tangible computer readable medium of EC110, wherein the unitsof higher-level redundancy information are not computable as a remainderof a polynomial division by a generator polynomial of correspondingbytes of the units of data storage information.

EC115) The tangible computer readable medium of EC110, wherein theaccumulating comprises accumulating at least a portion of the weightedsum incrementally.

EC116) The tangible computer readable medium of EC115, wherein theaccumulating further comprises processing more than one of the units ofdata storage information in parallel.

EC117) The tangible computer readable medium of EC116, wherein the morethan one of the units correspond to one or more integral numbers ofpages of one or more flash memories.

EC118) The tangible computer readable medium of EC110, wherein theaccumulating comprises accumulating at least a portion of the weightedsum in an ordering corresponding to an ordering of read operationcompletion by one or more flash memories.

EC119) The tangible computer readable medium of EC110, wherein theaccumulating comprises accumulating at least a portion of the weightedsum in an ordering corresponding to an ordering of data returned fromone or more flash memories.

EC120) The tangible computer readable medium of EC119, wherein theordering of data returned is based at least in part on an order thatdata is available from the one or more flash memories.

EC121) The tangible computer readable medium of EC110, wherein theaccumulating comprises accumulating at least a portion of the weightedsum in parallel.

EC122) The tangible computer readable medium of EC110, wherein theaccumulating comprises accumulating at least a portion of the weightedsum in parallel, the portion corresponding to elements of the units ofdata storage information that are retrievable from corresponding pagesof one or more flash memories.

EC123) The tangible computer readable medium of EC122, wherein theelements are determined, at least in part, by an order of completion ofread operations of the corresponding pages.

EC124) The tangible computer readable medium of EC111, wherein theoperations further comprise managing determining if one or more of theportions have a lower-level error correction failure when read.

EC125) The tangible computer readable medium of EC111, wherein theoperations further comprise managing reading one or more of theportions.

EC126) The tangible computer readable medium of EC110, wherein theaccumulating a weighted sum is selectively excludes from the weightedsum up to two of the units of data storage information.

EC127) The tangible computer readable medium of EC126, wherein theoperations further comprise managing processing results of theaccumulating to restore the excluded units of the data storageinformation.

EC128) The tangible computer readable medium of EC126, wherein theaccumulating comprises accumulating at least a portion of the weightedsum incrementally and in an ordering corresponding to an ordering ofread operation completion by one or more non-volatile memory devices.

EC129) The tangible computer readable medium of EC126, wherein theaccumulating comprises accumulating at least a portion of the weightedsum incrementally and in an ordering corresponding to an ordering ofdata returned from one or more non-volatile memory devices.

EC130) The tangible computer readable medium of EC129, wherein theordering of data returned is based at least in part on an order thatdata is available from the one or more non-volatile memory devices.

EC131) The tangible computer readable medium of EC110, wherein the unitsof higher-level redundancy information and the units of data storageinformation correspond to respective pages of one or more flashmemories.

EC132) The tangible computer readable medium of EC131, wherein the flashmemories are comprised of a plurality of die, and each of the respectivepages are on a unique one of the die.

EC133) The tangible computer readable medium of EC110, wherein theoperations further comprise managing storing the units of higher-levelredundancy information and the units of data storage information inportions of one or more flash memories at least in part in response torequests from a computing host.

EC134) The tangible computer readable medium of EC133, wherein theoperations further comprise managing interfacing the requests with thecomputing host.

EC135) The tangible computer readable medium of EC134, wherein theinterfacing the requests with the computing host is compatible with astorage interface standard.

EC136) The tangible computer readable medium of EC133, wherein thestoring comprises interfacing with the flash memories.

EC137) The tangible computer readable medium of EC136, wherein theinterfacing with the flash memories comprises a flash memory interface.

EC138) The tangible computer readable medium of EC133, wherein theoperations further comprise:

-   -   managing interfacing the requests with the computing host at        least in part via managing computing host interface logic        circuitry; and    -   wherein the storing is at least in part via flash memory        interface logic circuitry enabled to interface with the flash        memories.

EC139) The tangible computer readable medium of EC138, wherein thecomputing host interface logic circuitry and the flash memory interfacelogic circuitry are collectively implemented in a single IntegratedCircuit (IC).

EC140) The tangible computer readable medium of EC138, wherein thecomputing host interface logic circuitry and the flash memory interfacelogic circuitry are comprised in a Solid-State Disk (SSD).

EC141) The tangible computer readable medium of EC133, wherein theoperations further comprise managing operating all or any portions ofthe computing host.

EC142) The tangible computer readable medium of EC112, wherein theoperations further comprise managing operating at least one of the flashmemories.

EC143) A method comprising:

-   -   computing one or more pages of higher-level redundancy        information based at least in part on a plurality of pages of        data storage information;    -   storing the pages of higher-level redundancy information and the        pages of data storage information in pages of one or more flash        memories; and    -   wherein the computing comprises accumulating a weighted sum of a        respective non-zero unique constant value for each of the pages        of data storage information multiplied by contents of the pages        of data storage information as at least a portion of the pages        of higher-level redundancy information.

EC144) The method of EC143, wherein the pages of higher-level redundancyinformation are not computable as a remainder of a polynomial divisionby a generator polynomial of corresponding bytes of the pages of datastorage information.

EC145) The method of EC143, wherein the accumulating comprisesaccumulating incrementally.

EC146) The method of EC145, wherein the accumulating further comprisesprocessing at least partially in parallel more than one of the pages ofdata storage information.

EC147) The method of EC143, further comprising reading at least somepages stored in the flash memories; and determining if any of the pagesread are uncorrectable via lower-level redundancy information.

EC148) The method of EC143, further comprising computing a correctionversion of the higher-level redundancy information, wherein thecomputing a correction version of the higher-level redundancyinformation selectively excludes up to two pages of the pages of datastorage information.

EC149) The method of EC148, further comprising processing results of thecomputing a correction version of the higher-level redundancyinformation to restore the excluded pages of the data storageinformation.

EC150) The method of EC148, wherein the accumulating comprisesaccumulating incrementally at least partially in an order determined atleast in part by an order that read operations are completed by theflash memories.

EC151) The method of EC143, wherein the flash memories are comprised ofa plurality of die, and only one of the pages of the higher-levelredundancy information or the data storage information is stored in anyone of the die.

EC152) The method of EC151, wherein the pages of the higher-levelredundancy information are excluded from at least one of the die.

EC153) The method of EC151, wherein the pages of the data storageinformation are excluded from at least one of the die.

EC154) Any of the foregoing ECs having or referring to a storageinterface standard, wherein the storage interface standard comprises oneor more of

-   -   a Universal Serial Bus (USB) interface standard,    -   a Compact Flash (CF) interface standard,    -   a MultiMediaCard (MMC) interface standard,    -   an embedded MMC (eMMC) interface standard,    -   a Thunderbolt interface standard,    -   a UFS interface standard,    -   a Secure Digital (SD) interface standard,    -   a Memory Stick interface standard,    -   an xD-picture card interface standard,    -   an Integrated Drive Electronics (IDE) interface standard,    -   a Serial Advanced Technology Attachment (SATA) interface        standard,    -   an external SATA (eSATA) interface standard.    -   a Small Computer System Interface (SCSI) interface standard,    -   a Serial Attached Small Computer System Interface (SAS)        interface standard,    -   a Fibre Channel interface standard,    -   an Ethernet interface standard, and    -   a Peripheral Component Interconnect express (PCIe) interface        standard.

EC155) Any of the foregoing ECs having or referring to a flash memoryinterface, wherein the flash memory interface is compatible with one ormore of

-   -   an Open NAND Flash Interface (ONFI),    -   a Toggle-mode interface,    -   a Double-Data-Rate (DDR) synchronous interface,    -   a DDR2 synchronous interface;    -   a synchronous interface, and    -   an asynchronous interface.

EC156) Any of the foregoing ECs having or referring to a computing host,wherein the computing host comprises one or more of

-   -   a computer,    -   a workstation computer,    -   a server computer,    -   a storage server,    -   a Storage Attached Network (SAN),    -   a Network Attached Storage (NAS) device,    -   a Direct Attached Storage (DAS) device,    -   a storage appliance,    -   a Personal Computer (PC),    -   a laptop computer.    -   a notebook computer,    -   a netbook computer,    -   a tablet device or computer,    -   an ultrabook computer,    -   an electronic reading device (an e-reader),    -   a Personal Digital Assistant (PDA),    -   a navigation system,    -   a (handheld) Global Positioning System (GPS) device,    -   an automotive control system    -   an automotive media control system or computer,    -   a printer, copier or fax machine or all-in-one device,    -   a Point Of Sale POS device,    -   a cash-register,    -   a media player,    -   a television,    -   a media recorder.    -   a Digital Video Recorder (DVR),    -   a digital camera,    -   a cellular handset,    -   a cordless telephone handset, and    -   an electronic game.

EC157) Any of the foregoing ECs having or referring to at least oneflash memory, wherein at least a portion of the at least one flashmemory comprises one or more of

-   -   NAND flash technology storage cells, and    -   NOR flash technology storage cells.

EC158) Any of the foregoing ECs having or referring to at least oneflash memory, wherein at least a portion of the at least one flashmemory comprises one or more of

-   -   Single-Level Cell (SLC) flash technology storage cells, and    -   Multi-Level Cell (MLC) flash technology storage cells.

EC159) Any of the foregoing FCs having or referring to at least oneflash memory, wherein at least a portion of the at least one flashmemory comprises one or more of

-   -   polysilicon technology-based charge storage cells, and    -   silicon nitride technology-based charge storage cells.

EC160) Any of the foregoing ECs having or referring to at least oneflash memory, wherein at least a portion of the at least one flashmemory comprises one or more of

-   -   two-dimensional technology-based flash memory technology, and    -   three-dimensional technology-based flash memory technology.

System

In some embodiments, an I/O device, such as an SSD, includes an SSDcontroller. The SSD controller acts as a bridge between the hostinterface and NVM of the SSD, and executes commands of a host protocolsent from a computing host via a host interface of the SSD. At leastsome of the commands direct the SSD to write and read the NVM with datasent from and to the computing host, respectively. In furtherembodiments, the SSD controller is enabled to use a map to translatebetween LBAs of the host protocol and physical storage addresses in theNVM. In further embodiments, at least a portion of the map is used forprivate storage (not visible to the computing host) of the I/O device.For example, a portion of the LBAs not accessible by the computing hostis used by the I/O device to manage access to logs, statistics, or otherprivate data.

In some embodiments, accessing compressed data of varying-sized quantain NVM provides improved storage efficiency in some usage scenarios. Forexample, an SSD controller receives (uncompressed) data from a computinghost (e.g., relating to a disk write command), compresses the data, andstores the compressed data into flash memory. In response to asubsequent request from the computing host (e.g., relating to a diskread command), the SSD controller reads the compressed data from theflash memory, uncompresses the compressed data, and provides theuncompressed data to the computing host. The compressed data is storedin the flash memory according to varying-sized quanta, the quanta sizevarying due to, e.g., compression algorithm, operating mode, andcompression effectiveness on various data. The SSD controlleruncompresses the data in part by consulting an included map table todetermine where header(s) are stored in the flash memory. The SSDcontroller parses the header(s) obtained from the flash memory todetermine where appropriate (compressed) data is stored in the flashmemory. The SSD controller uncompresses the appropriate data from theflash memory to produce the uncompressed data to provide to thecomputing host. In the instant application, uncompress (and variantsthereof) is synonymous with decompress (and variants thereof).

In various embodiments, an SSD controller includes a host interface forinterfacing with a computing host, an interface for interfacing with NVMsuch as flash memory, and circuitry for controlling the interfaces andperforming (and/or controlling various aspects of the performing)compressing and uncompressing, as well as lower-level redundancy and/orerror correction, higher-level redundancy and/or error correction, anddynamic higher-level redundancy mode management with independent siliconelements.

According to various embodiments, some host interfaces are compatiblewith one or more of a USB interface standard, a CF interface standard,an MMC interface standard, an eMMC interface standard, a Thunderboltinterface standard, a UFS interface standard, an SD interface standard,a Memory Stick interface standard, an xD-picture card interfacestandard, an IDE interface standard, a SATA interface standard, a SCSIinterface standard, a SAS interface standard, and a PCIe interfacestandard. According to various embodiments, the computing host is all orany portions of a computer, a workstation computer, a server computer, astorage server, a SAN, a NAS device, a DAS device, a storage appliance,a PC, a laptop computer, a notebook computer, a netbook computer, atablet device or computer, an ultrabook computer, an electronic readingdevice (such as an e-reader), a PDA, a navigation system, a (handheld)GPS device, an automotive control system, an automotive media controlsystem or computer, a printer, copier or fax machine or all-in-onedevice, a POS device, a cash-register, a media player, a television, amedia recorder, a DVR, a digital camera, a cellular handset, a cordlesstelephone handset, and an electronic game. In some embodiments, aninterfacing host (such as a SAS/SATA bridge) operates as a computinghost and/or as a bridge to a computing host.

In various embodiments, the SSD controller includes one or moreprocessors. The processors execute firmware to control and/or performoperation of the SSD controller. The SSD controller communicates withthe computing host to send and receive commands and/or status as well asdata. The computing host executes one or more of an operating system, adriver, and an application. Communication by the computing host with theSSD controller is optionally and/or selectively via the driver and/orvia the application. In a first example, all communication to the SSDcontroller is via the driver, and the application provides higher-levelcommands to the driver that the driver translates into specific commandsfor the SSD controller. In a second example, the driver implements abypass mode and the application is enabled to send specific commands tothe SSD controller via the driver. In a third example, a PCIe SSDcontroller supports one or more Virtual Functions (VFs), enabling anapplication, once configured, to communicate directly with the SSDcontroller, bypassing the driver.

According to various embodiments, some SSDs are compatible withform-factors, electrical interfaces, and/or protocols used by magneticand/or optical non-volatile storage, such as HDDs, CD drives, and DVDdrives. In various embodiments, SSDs use various combinations of zero ormore parity codes, zero or more RS codes, zero or more BCH codes, zeroor more Viterbi or other trellis codes, and zero or more LDPC codes.

FIG. 1A illustrates selected details of an embodiment of an SSDincluding an SSD controller providing fractional higher-level redundancyfor NVMs (e.g. flash memories, such as NAND flash memories). The SSDcontroller is for managing non-volatile storage, such as implemented viaNVM elements (e.g., flash memories). SSD Controller 100 iscommunicatively coupled via one or more External Interfaces 110 to ahost (not illustrated). According to various embodiments, ExternalInterfaces 110 are one or more of: a SATA interface; a SAS interface; aPCIe interface; a Fibre Channel interface; an Ethernet Interface (suchas 10 Gigabit Ethernet); a non-standard version of any of the precedinginterfaces; a custom interface; or any other type of interface used tointerconnect storage and/or communications and/or computing devices. Forexample, in some embodiments, SSD Controller 100 includes a SATAinterface and a PCIe interface.

SSD Controller 100 is further communicatively coupled via one or moreDevice Interfaces 190 to NVM 199 including one or more storage devices,such as one or more instances of Flash Device 192. According to variousembodiments, Device Interfaces 190 are one or more of: an asynchronousinterface; a synchronous interface; a single-data-rate (SDR) interface;a double-data-rate (DDR) interface; a DRAM-compatible DDR or DDR2synchronous interface; an ONFI compatible interface, such as an ONFI 2.2or ONFI 3.0 compatible interface; a Toggle-mode compatible flashinterface; a non-standard version of any of the preceding interfaces; acustom interface; or any other type of interface used to connect tostorage devices.

Each of Flash Device 192 has, in some embodiments, one or moreindividual Flash Die 194. According to type of a particular one of FlashDevice 192, a plurality of Flash Die 194 in the particular Flash Device192 is optionally and/or selectively accessible in parallel. FlashDevice 192 is merely representative of one type of storage deviceenabled to communicatively couple to SSD Controller 100. In variousembodiments, any type of storage device is usable, such as an SLC NANDflash memory, MLC NAND flash memory, NOR flash memory, flash memoryusing polysilicon or silicon nitride technology-based charge storagecells, two- or three-dimensional technology-based flash memory,read-only memory, static random access memory, dynamic random accessmemory, ferromagnetic memory, phase-change memory, racetrack memory,ReRAM, or any other type of memory device or storage medium.

According to various embodiments, Device Interfaces 190 are organizedas: one or more busses with one or more instances of Flash Device 192per bus; one or more groups of busses with one or more instances ofFlash Device 192 per bus, having busses in a group generally accessed inparallel; or any other organization of one or more instances of FlashDevice 192 onto Device Interfaces 190.

Continuing in FIG. 1A, SSD Controller 100 has one or more modules, suchas Host Interfaces 111, Data Processing 121, Buffer 131, Map 141,Recycler 151, ECC 161, Device Interface Logic 191, and CPU 171. Thespecific modules and interconnections illustrated in FIG. 1A are merelyrepresentative of one embodiment, and many arrangements andinterconnections of some or all of the modules, as well as additionalmodules not illustrated, are conceived. In a first example, in someembodiments, there are two or more Host Interfaces 111 to providedual-porting. In a second example, in some embodiments, Data Processing121 and/or ECC 161 are combined with Buffer 131. In a third example, insome embodiments, Host Interfaces 111 is directly coupled to Buffer 131,and Data Processing 121 optionally and/or selectively operates on datastored in Buffer 131. In a fourth example, in some embodiments, DeviceInterface Logic 191 is directly coupled to Buffer 131, and ECC 161optionally and/or selectively operates on data stored in Buffer 131.

Host Interfaces 111 sends and receives commands and/or data via ExternalInterfaces 110, and, in some embodiments, tracks progress of individualcommands via Tag Tracking 113. For example, the commands include a readcommand specifying an address (such as an LBA) and an amount of data(such as a number of LBA quanta, e.g., sectors) to read; in response theSSD provides read status and/or read data. For another example, thecommands include a write command specifying an address (such as an LBA)and an amount of data (such as a number of LBA quanta, e.g., sectors) towrite; in response the SSD provides write status and/or requests writedata and optionally subsequently provides write status. For yet anotherexample, the commands include a de-allocation command (e.g. a trimcommand) specifying one or more addresses (such as one or more LBAs)that no longer need be allocated; in response the SSD modifies the Mapaccordingly and optionally provides de-allocation status. In somecontexts an ATA compatible TRIM command is an exemplary de-allocationcommand. For yet another example, the commands include a super capacitortest command or a data hardening success query; in response, the SSDprovides appropriate status. In some embodiments, Host Interfaces 111 iscompatible with a SATA protocol and, using NCQ commands, is enabled tohave up to 32 pending commands, each with a unique tag represented as anumber from 0 to 31. In some embodiments, Tag Tracking 113 is enabled toassociate an external tag for a command received via External Interfaces110 with an internal tag used to track the command during processing bySSD Controller 100.

According to various embodiments, one or more of: Data Processing 121optionally and/or selectively processes some or all data sent betweenBuffer 131 and External Interfaces 110; and Data Processing 121optionally and/or selectively processes data stored in Buffer 131. Insome embodiments, Data Processing 121 uses one or more Engines 123 toperform one or more of: formatting; reformatting; transcoding; and anyother data processing and/or manipulation task.

Buffer 131 stores data sent to/from External Interfaces 110 from/toDevice Interfaces 190. In some embodiments, Buffer 131 additionallystores system data, such as some or all map tables, used by SSDController 100 to manage one or more instances of Flash Device 192. Invarious embodiments, Buffer 131 has one or more of: Memory 137 used fortemporary storage of data; DMA 133 used to control movement of data toand/or from Buffer 131; and ECC-X 135 used to provide higher-level errorcorrection and/or redundancy functions; and other data movement and/ormanipulation functions. An example of a higher-level redundancy functionis a RAID-likc capability (e.g. RASIE, such as fractional RASIE and/ornon-fractional RASIE, described in further detail elsewhere herein);with redundancy at a flash device level (e.g., multiple ones of FlashDevice 192) and/or a flash die level (e.g., Flash Die 194) instead of ata disk level.

According to various embodiments, one or more of: ECC 161 optionallyand/or selectively processes some or all data sent between Buffer 131and Device Interfaces 190; and ECC 161 optionally and/or selectivelyprocesses data stored in Buffer 131. In some embodiments, ECC 161 isused to provide lower-level error correction and/or redundancyfunctions, such as in accordance with one or more ECC techniques. Insome embodiments, ECC implements one or more of: a CRC code; a Hammingcode; an RS code; a BCH code; an LDPC code; a Viterbi code; a trelliscode; a hard-decision code; a soft-decision code; an erasure-based code;any error detecting and/or correcting code; and any combination of thepreceding. In some embodiments. ECC 161 includes one or more decoders(such as LDPC decoders).

Device Interface Logic 191 controls instances of Flash Device 192 viaDevice Interfaces 190. Device Interface Logic 191 is enabled to senddata to/from the instances of Flash Device 192 according to a protocolof Flash Device 192. Device Interface Logic 191 includes Scheduling 193to selectively sequence control of the instances of Flash Device 192 viaDevice Interfaces 190. For example, in some embodiments, Scheduling 193is enabled to queue operations to the instances of Flash Device 192, andto selectively send the operations to individual ones of the instancesof Flash Device 192 (or Flash Die 194) as individual ones of theinstances of Flash Device 192 (or Flash Die 194) are available.

Map 141 converts between data addressing used on External Interfaces 110and data addressing used on Device Interfaces 190, using Table 143 tomap external data addresses to locations in NVM 199. For example, insome embodiments, Map 141 converts LBAs used on External Interfaces 110to block and/or page addresses targeting one or more Flash Die 194, viamapping provided by Table 143. For LBAs that have never been writtensince drive manufacture or de-allocation, the Map points to a defaultvalue to return if the LBAs are read. For example, when processing ade-allocation command, the Map is modified so that entries correspondingto the de-allocated LBAs point to one of the default values. In variousembodiments, there are various default values, each having acorresponding pointer. The plurality of default values enables readingsome de-allocated LBAs (such as in a first range) as one default value,while reading other de-allocated LBAs (such as in a second range) asanother default value. The default values, in various embodiments, aredefined by flash memory, hardware, firmware, command and/or primitivearguments and/or parameters, programmable registers, or variouscombinations thereof.

In some embodiments, Map 141 uses Table 143 to perform and/or to look uptranslations between addresses used on External Interfaces 110 and dataaddressing used on Device Interfaces 190. According to variousembodiments, Table 143 is one or more of: a one-level map; a two-levelmap; a multi-level map; a map cache; a compressed map; any type ofmapping from one address space to another; and any combination of theforegoing. According to various embodiments, Table 143 includes one ormore of: static random access memory; dynamic random access memory; NVM(such as flash memory); cache memory; on-chip memory; off-chip memory;and any combination of the foregoing.

In some embodiments. Recycler 151 performs garbage collection. Forexample, in some embodiments, instances of Flash Device 192 containblocks that must be erased before the blocks are re-writeable. Recycler151 is enabled to determine which portions of the instances of FlashDevice 192 are actively in use (e.g., allocated instead ofde-allocated), such as by scanning a map maintained by Map 141, and tomake unused (e.g., de-allocated) portions of the instances of FlashDevice 192 available for writing by erasing the unused portions. Infurther embodiments, Recycler 151 is enabled to move data stored withininstances of Flash Device 192 to make larger contiguous portions of theinstances of Flash Device 192 available for writing.

In some embodiments, instances of Flash Device 192 are selectivelyand/or dynamically configured, managed, and/or used to have one or morebands for storing data of different types and/or properties. A number,arrangement, size, and type of the bands are dynamically changeable. Forexample, data from a computing host is written into a hot (active) band,while data from Recycler 151 is written into a cold (less active) band.In some usage scenarios, if the computing host writes a long, sequentialstream, then a size of the hot band grows, whereas if the computing hostdoes random writes or few writes, then a size of the cold band grows.

CPU 171 controls various portions of SSD Controller 100. CPU 171includes CPU Core 172. CPU Core 172 is, according to variousembodiments, one or more single-core or multi-core processors. Theindividual processors cores in CPU Core 172 are, in some embodiments,multi-threaded. CPU Core 172 includes instruction and/or data cachesand/or memories. For example, the instruction memory containsinstructions to enable CPU Core 172 to execute programs (e.g. softwaresometimes called firmware) to control SSD Controller 100. In someembodiments, some or all of the firmware executed by CPU Core 172 isstored on instances of Flash Device 192 (as illustrated, e.g., asFirmware 106 of NVM 199 in FIG. 1B).

In various embodiments, CPU 171 further includes: Command Management 173to track and control commands received via External Interfaces 110 whilethe commands are in progress; Buffer Management 175 to controlallocation and use of Buffer 131; Translation Management 177 to controlMap 141; Coherency Management 179 to control consistency of dataaddressing and to avoid conflicts such as between external data accessesand recycle data accesses; Device Management 181 to control DeviceInterface Logic 191; Identity Management 182 to control modification andcommunication of identify information, and optionally other managementunits. None, any, or all of the management functions performed by CPU171 are, according to various embodiments, controlled and/or managed byhardware, by software (such as firmware executing on CPU Core 172 or ona host connected via External Interfaces 110), or any combinationthereof.

In some embodiments, CPU 171 is enabled to perform other managementtasks, such as one or more of: gathering and/or reporting performancestatistics; implementing SMART; controlling power sequencing,controlling and/or monitoring and/or adjusting power consumption;responding to power failures; controlling and/or monitoring and/oradjusting clock rates; and other management tasks.

Various embodiments include a computing-host flash memory controllerthat is similar to SSD Controller 100 and is compatible with operationwith various computing hosts, such as via adaptation of Host Interfaces111 and/or External Interfaces 110. The various computing hosts includeone or any combination of a computer, a workstation computer, a servercomputer, a storage server, a SAN, a NAS device, a DAS device, a storageappliance, a PC, a laptop computer, a notebook computer, a netbookcomputer, a tablet device or computer, an ultrabook computer, anelectronic reading device (such as an e-reader), a PDA, a navigationsystem, a (handheld) GPS device, an automotive control system, anautomotive media control system or computer, a printer, copier or faxmachine or all-in-one device, a POS device, a cash-register, a mediaplayer, a television, a media recorder, a DVR, a digital camera, acellular handset, a cordless telephone handset, and an electronic game.

In various embodiments, all or any portions of an SSD controller (or acomputing-host flash memory controller) are implemented on a single IC,a single dic of a multi-die IC, a plurality of dice of a multi-die IC,or a plurality of ICs. For example, Buffer 131 is implemented on a samedie as other elements of SSD Controller 100. For another example, Buffer131 is implemented on a different die than other elements of SSDController 100.

FIG. 1B illustrates selected details of various embodiments of systemsincluding one or more instances of the SSD of FIG. 1A. SSD 101 includesSSD Controller 100 coupled to NVM 199 via Device Interfaces 190. Thefigure illustrates various classes of embodiments: a single SSD coupleddirectly to a host, a plurality of SSDs each respectively coupleddirectly to a host via respective external interfaces, and one or moreSSDs coupled indirectly to a host via various interconnection elements.

As an example embodiment of a single SSD coupled directly to a host, oneinstance of SSD 101 is coupled directly to Host 102 via ExternalInterfaces 110 (e.g. Switch/Fabric/Intermediate Controller 103 isomitted, bypassed, or passed-through). As an example embodiment of aplurality of SSDs each coupled directly to a host via respectiveexternal interfaces, each of a plurality of instances of SSD 101 isrespectively coupled directly to Host 102 via a respective instance ofExternal Interfaces 110 (e.g. Switch/Fabric/Intermediate Controller 103is omitted, bypassed, or passed-through). As an example embodiment ofone or more SSDs coupled indirectly to a host via variousinterconnection elements, each of one or more instances of SSD 101 isrespectively coupled indirectly to Host 102. Each indirect coupling isvia a respective instance of External Interfaces 110 coupled toSwitch/Fabric/Intermediate Controller 103, and Intermediate Interfaces104 coupling to Host 102.

Some of the embodiments including Switch/Fabric/Intermediate Controlleralso include Card Memory 112C coupled via Memory Interface 180 andaccessible by the SSDs. In various embodiments, one or more of the SSDs,the Switch/Fabric/Intermediate Controller, and/or the Card Memory areincluded on a physically identifiable module, card, or pluggable element(e.g. I/O Card 116). In some embodiments, SSD 101 (or variationsthereof) corresponds to a SAS drive or a SATA drive that is coupled toan initiator operating as Host 102.

Host 102 is enabled to execute various elements of Host Software 115,such as various combinations of OS 105. Driver 107. Application 109, andMulti-Device Management Software 114. Dotted-arrow 107D isrepresentative of Host Software←→ I/O Device Communication, e.g. datasent/received to/from one or more of the instances of SSD 101 andfrom/to any one or more of OS 105 via Driver 107, Driver 107, andApplication 109, either via Driver 107, or directly as a VF.

OS 105 includes and/or is enabled to operate with drivers (illustratedconceptually by Driver 107) for interfacing with the SSD. Variousversions of Windows (e.g. 95, 98, ME, NT, XP, 2000, Server, Vista, and7), various versions of Linux (e.g. Red Hat, Debian, and Ubuntu), andvarious versions of MacOS (e.g. 8, 9 and X) are examples of OS 105. Invarious embodiments, the drivers are standard and/or generic drivers(sometimes termed “shrink-wrapped” or “pre-installed”) operable with astandard interface and/or protocol such as SATA, AIICI, or NVM Express,or are optionally customized and/or vendor specific to enable use ofcommands specific to SSD 101. Some drives and/or drivers havepass-through modes to enable application-level programs, such asApplication 109 via Optimized NAND Access (sometimes termed ONA) orDirect NAND Access (sometimes termed DNA) techniques, to communicatecommands directly to SSD 101, enabling a customized application to usecommands specific to SSD 101 even with a generic driver. ONA techniquesinclude one or more of: use of non-standard modifiers (hints); use ofvendor-specific commands; communication of non-standard statistics, suchas actual NVM usage according to compressibility; and other techniques.DNA techniques include one or more of: use of non-standard commands orvendor-specific providing unmapped read, write, and/or erase access tothe NVM; use of non-standard or vendor-specific commands providing moredirect access to the NVM, such as by bypassing formatting of data thatthe I/O device would otherwise do; and other techniques. Examples of thedriver are a driver without ONA or DNA support, an ONA-enabled driver, aDNA-enabled driver, and an ONA/DNA-enabled driver. Further examples ofthe driver are a vendor-provided, vendor-developed, and/orvendor-enhanced driver, and a client-provided, client-developed, and/orclient-enhanced driver.

Examples of the application-level programs are an application withoutONA or DNA support, an ONA-enabled application, a DNA-enabledapplication, and an ONA/DNA-enabled application. Dotted-arrow 109D isrepresentative of Application←→ I/O Device Communication (e.g. bypassvia a driver or bypass via a VF for an application), e.g. an ONA-enabledapplication and an ONA-enabled driver communicating with an SSD, such aswithout the application using the OS as an intermediary. Dotted-arrow109V is representative of Application←→ I/O Device Communication (e.g.bypass via a VF for an application), e.g. a DNA-enabled application anda DNA-enabled driver communicating with an SSD, such as without theapplication using the OS or the driver as intermediaries.

One or more portions of NVM 199 are used, in some embodiments, forfirmware storage, e.g. Firmware 106. The firmware storage includes oneor more firmware images (or portions thereof). A firmware image has, forexample, one or more images of firmware, executed, e.g., by CPU Core 172of SSD Controller 100. A firmware image has, for another example, one ormore images of constants, parameter values, and NVM device information,referenced, e.g. by the CPU core during the firmware execution. Theimages of firmware correspond, e.g., to a current firmware image andzero or more previous (with respect to firmware updates) firmwareimages. In various embodiments, the firmware provides for generic,standard, ONA, and/or DNA operating modes. In some embodiments, one ormore of the firmware operating modes are enabled (e.g. one or more APIsare “unlocked”) via keys or various software techniques, optionallycommunicated and/or provided by a driver.

In some embodiments lacking the Switch/Fabric/Intermediate Controller,the SSD is coupled to the Host directly via External Interfaces 110. Invarious embodiments. SSD Controller 100 is coupled to the Host via oneor more intermediate levels of other controllers, such as a RAIDcontroller. In some embodiments, SSD 101 (or variations thereof)corresponds to a SAS drive or a SATA drive andSwitch/Fabric/Intermediate Controller 103 corresponds to an expanderthat is in turn coupled to an initiator, or alternativelySwitch/Fabric/Intermediate Controller 103 corresponds to a bridge thatis indirectly coupled to an initiator via an expander. In someembodiments, Switch/Fabric/Intermediate Controller 103 includes one ormore PCIe switches and/or fabrics.

In various embodiments, such as some of the embodiments with Host 102 asa computing host (e.g. a computer, a workstation computer, a servercomputer, a storage server, a SAN, a NAS device, a DAS device, a storageappliance, a PC, a laptop computer, a notebook computer, and/or anetbook computer), the computing host is optionally enabled tocommunicate (e.g. via optional I/O & Storage Devices/Resources 117 andoptional LAN/WAN 119) with one or more local and/or remote servers (e.g.optional Servers 118). The communication enables, for example, localand/or remote access, management, and/or usage of any one or more of SSD101 elements. In some embodiments, the communication is wholly orpartially via Ethernet. In some embodiments, the communication is whollyor partially via Fibre Channel. LAN/WAN 119 is representative, invarious embodiments, of one or more Local and/or Wide Area Networks,such as any one or more of a network in a server farm, a networkcoupling server farms, a metro-area network, and the Internet.

In various embodiments, an SSD controller and/or a computing-host flashmemory controller in combination with one or more NVMs are implementedas a non-volatile storage component, such as a USB storage component, aCF storage component, an MMC storage component, an eMMC storagecomponent, a Thunderbolt storage component, a UFS storage component, anSD storage component, a Memory Stick storage component, and anxD-picture card storage component.

In various embodiments, all or any portions of an SSD controller (or acomputing-host flash memory controller), or functions thereof, areimplemented in a host that the controller is to be coupled with (e.g.,Host 102 of FIG. 1B). In various embodiments, all or any portions of anSSD controller (or a computing-host flash memory controller), orfunctions thereof, are implemented via hardware (e.g., logic circuitry),software and/or firmware (e.g., driver software and/or SSD controlfirmware), or any combination thereof. For example, functionality of orassociated with an FCC unit (such as similar to FCC 161 and/or ECC-X 135of FIG. 1A) is implemented partially via software on a host andpartially via a combination of firmware and hardware in an SSDcontroller. For another example, functionality of or associated with arecycler unit (such as similar to Recycler 151 of FIG. 1A) isimplemented partially via software on a host and partially via hardwarein a computing-host flash memory controller.

Mapping Operation

FIG. 2 illustrates selected details of an embodiment of mapping an LPNportion of an LBA. In some embodiments, a read unit is a finestgranularity of an NVM that is independently readable, such as a portionof a page of the NVM. In further embodiments, the read unit correspondsto check bits (sometimes-termed redundancy) of a (lower-level)error-correcting code along with all data protected by the check bits.For example, ECC 161 of FIG. 1A implements error correction via checkbits such as via an LDPC code, and a read unit corresponds to codingbits implementing the LDPC code in addition to data bits protected bythe LDPC coding bits.

In some embodiments. Map 141 maps LPN 213 portion of LBA 211 to Map Infofor LPN 221, such as via Table 143 (as illustrated in FIG. 1A). Map infofor an LPN (such as Map Info for LPN 221) is sometimes termed a mapentry. Map 141 is said to associate an LPN with a corresponding mapentry. In various embodiments, mapping is via one or more associativelook-ups, via one or more non-associative look-ups, and/or via one ormore other techniques.

In some embodiments, SSD Controller 100 maintains one map entry for eachLPN potentially and/or actively in use.

In some embodiments, Map Info for LPN 221 includes respective Read UnitAddress 223 and Length in Read Units 225. In some embodiments, a lengthand/or a span are stored encoded, such as by storing the length as anoffset from the span, e.g. in all or any portions of Length in ReadUnits 225. In further embodiments, a first LPN is associated with afirst map entry, a second LPN (different from the first LPN, butreferring to a logical page of a same size as a logical page referred toby the first LPN) is associated with a second map entry, and therespective length in read units of the first map entry is different fromthe respective length in read units of the second map entry.

In various embodiments, at a same point in time, a first LPN isassociated with a first map entry, a second LPN (different from thefirst LPN) is associated with a second map entry, and the respectiveread unit address of the first map entry is the same as the respectiveread unit address of the second map entry. In further embodiments, dataassociated with the first LPN and data associated with the second LPNare both stored in a same physical page of a same device in NVM 199.

According to various embodiments, Read Unit Address 223 is associatedwith one or more of: a starting address in the NVM; an ending address inthe NVM; an offset of any of the preceding; and any other techniques foridentifying a portion of the NVM associated with LPN 213.

FIG. 3 illustrates selected details of an embodiment of accessing an NVMat a read unit address to produce read data organized as various readunits, collectively having a length measured in quanta of read units.According to various embodiments, First Read Unit is one or more of: aone of read units in Read Data 311 with a lowest address in an addressspace of the NVM; a fixed one of the read units; an arbitrary one of theread units; a variable one of the read units; and a one of the readunits selected by any other technique. In various embodiments, SSDController 100 is enabled to access NVM 199 and produce Read Data 311 byreading no more than a number of read units specified by Length in ReadUnits 225.

FIG. 4A illustrates selected details of an embodiment of a read unit(such as Read Units 313 or 315 of FIG. 3) as Read Unit 401A. In variousembodiments and/or usage scenarios, Header 1 411A through Header N 419Aare contiguous, and respective data regions identified (such as viarespective offsets) by each of the headers are contiguous following alast one of the headers. The data regions collectively form Data Bytes421A. The data regions are stored in a location order that matches thelocation order the headers are stored. For example, consider a firstheader, at the beginning of a read unit, with a second header and athird header contiguously following the first header. A first dataregion (identified by a first offset in the first header) contiguouslyfollows the third header. A second data region (identified by a secondoffset in the second header) contiguously follows the first data region.Similarly, a third data region (identified by the third header)contiguously follows the second data region.

FIG. 4B illustrates selected details of another embodiment of a readunit (such as Read Units 313 or 315 of FIG. 3) as Read Unit 401B. Invarious embodiments and/or usage scenarios, Header Marker (HM) 410B isan optional initial field (such as a one-byte field) indicating a numberof following contiguous headers (Header 1 411B, Header 2 412B . . .Header N 419B). Data regions (Data Bytes 421B, Data Bytes 422B . . .Data Bytes 429B) are identified respectively by the headers (Header 1411B, Header 2 412B . . . Header N 419B) and are stored in a locationorder that is opposite of the location order that the headers arestored. Headers start at the beginning of a read unit, whilecorresponding data regions start at the end of a read unit. In someembodiments, data bytes within a data region (e.g. Data Bytes 421B, DataBytes 422B . . . Data Bytes 429B) are arranged in a forward order (byteorder matching location order), while in other embodiments, the databytes are arranged in a reverse order (byte order reversed with respectto location order). In some embodiments, a header marker is used in readunits where headers and data bytes are stored in a same location order(e.g. as illustrated in FIG. 4A).

In some embodiments, Optional Padding Bytes 431A (or 431B) are accordingto granularity of data associated with a particular LPN. For example, insome embodiments, if Data Bytes 421A (or collectively Data Bytes 421B,Data Bytes 422B . . . Data Bytes 429B) have less than a fixed amount ofremaining space, such as 8 bytes, after storing data associated with allbut a last one of Header 1 411A through Header N 419A (or Header 1 411B,Header 2 412B . . . Header N 419B), then data for an LPN associated withthe last header starts in a subsequent read unit. In furtherembodiments, a particular offset value (e.g. all ones) in the lastheader indicates that the data for the LPN associated with the lastheader starts in the subsequent read unit.

FIG. 5 illustrates selected details of an embodiment of a header (suchas any of Header 1 411A through Header N 419A of FIG. 4A or Header 1411B through Header 419B of FIG. 4B) having a number of fields. In someembodiments, headers are fixed-length (e.g. each header is a same numberof bytes long). Header 501 includes fields Type 511, Last Indicator 513,Flags 515, LPN 517, Length 519, and Offset 521. The type fieldidentifies a category of the data bytes. For example, the type fieldindicates the category of the data bytes is one of host data (e.g.logical page data) or system data (e.g. map information or checkpointinformation). The last field indicates that the header is the lastheader before the data bytes. In some embodiments with a header marker,the last field is optionally omitted. The LPN field is the LPN that theheader is associated with. The LPN field enables parsing of the headersto determine a particular one of the headers that is associated with aparticular LPN by, for example, searching the headers for one with anLPN field matching the particular LPN. The length field is the length,in bytes, of the data bytes (e.g. how many bytes of data there are inData Bytes 421A associated with Header 501). In some embodiments, anoffset in the offset field is rounded according to a particulargranularity (e.g. 8-byte granularity).

In various embodiments, some or all information associated with aparticular LPN is stored in a map entry associated with the particularLPN, a header associated with the particular LPN, or both. For example,in some embodiments, some or all of Length 519 is stored in a map entryrather than in a header.

FIG. 6 illustrates selected details of an embodiment of blocks, pages,and read units of multiple NVM devices (e.g. one or more flash dieand/or flash chips) managed in logical slices and/or sections. Themanagement functions include any one or more of reading, recycling,erasing, programming/writing, and other management functions. Thelogical slices and/or sections are sometimes referred to as R-blocks.The figure illustrates an embodiment with 66 flash die. Three of theflash die are explicitly illustrated (Flash Die 610.65, 610.1, and610.0) and 63 of the flash die are implicitly illustrated (610.64 . . .610.2).

Each of the flash die (such as any one of Flash Die 610.65 . . . 610.1,and 610.0) provides storage organized as blocks (such as Blocks 610.65BB. . . 610.65B1, and 610.65B0 of Flash Die 610.65; Blocks 610.0BB . . .610.0B1, and 610.0B0 of Flash Die 610.0; and so forth). The blocks inturn include pages (such as Pages 610.65PP . . . 610.65P1, and 610.65P0of Block 610.65B0; Pages 610.0PP . . . 610.0P1, and 610.0P0 of Block610.0B0; and so forth). The pages in turn include read units (such asRead Units 610.65RR . . . 610.65R1, and 610.65R0 of Page 610.65P0; ReadUnits 610.0RR . . . 610.0R1, and 610.0R0 of Page 610.0P0; and so forth).

In some embodiments, each flash die includes an integer number of blocks(e.g. N blocks) and a block is a smallest quantum of erasing. In someembodiments, each block includes an integer number of pages and a pageis a smallest quantum of writing. According to various embodiments, oneor more of: a read unit is a smallest quantum of reading and errorcorrection; each page includes an integer number of read units; anassociated group of two or more pages includes an integer number of readunits; and read units optionally and/or selectively span pageboundaries.

In various embodiments, various NVM management functions (e.g. reading,recycling, erasing, and/or programming/writing) are performed in unitsof R-blocks. An R-block is exemplified as a logical slice or sectionacross various die (e.g. all die, all die excluding ones that are whollyor partially failed, and/or one or more selected subsets of die) of,e.g., a flash memory. For example, in a flash memory having R flash die,each flash die having N blocks, each R-block is the i^(th) block fromeach of the flash die taken together, for a total of N R-blocks.Continuing with the example, if one of the R flash die fails, then eachR-block is the i^(th) block from each of the flash die except the failedflash die, for a total of N R-blocks, each R-block having one less blockthan before the failure. For another example, in a flash memory having Rflash die, each with N blocks, each R-block is the i^(th) and (i+1)^(th)block from each of the flash die, for a total of N/2 R-blocks. For yetanother example, in a flash memory having a plurality of dual planedevices, each R-block is the i^(th) even block and the i^(th) odd blockfrom each of the dual plane devices. For yet another example, in a flashmemory having a plurality of multi-plane devices, each R-block includesblocks selected to maximize parallelism (e.g. during programming)provided by the multi-plane devices. Note that in the aforementionedexample of R-blocks in dual plane devices, the dual-plane devices areexamples of multi-plane devices, and the R-blocks being the i^(th) evenblock and the i^(th) odd block from each of the dual plane devices is anexample of R-blocks including blocks selected to maximize parallelism.For yet another example, in a flash memory having R flash die, anR-block is k non-contiguous blocks, such as blocks i₁, i₂ . . . i_(k)from each of the R flash die. For a final example, in a flash memoryhaving R flash die, each with N blocks, each R-block is the i^(th)through (i+k−1)^(th) block from each of the flash die, for a total ofN/k R-blocks.

In various embodiments with blocks treated in pairs or other associatedgroups as part of forming an R-block, respective pages from each blockof an associated group of the blocks are also treated as a unit, atleast for writing, forming a larger multi-block page. For example,continuing the foregoing dual plane example, a first page of aparticular one of the even blocks and a first page of an associated oneof the odd blocks are treated as a unit for writing, and optionallyand/or selectively as a unit for reading. Similarly, a second page ofthe particular even block and a second page of the associated odd blockare treated as a unit. According to various embodiments, a page of NVMas used herein refers to one or more of: a single page of NVM; amulti-block page of NVM; a multi-block page of NVM for writing that isoptionally and/or selectively treated as one or more individual pagesfor reading; and any other grouping or association of pages of NVM.

The figure illustrates a plurality of illustrative R-blocks, three ofthem explicitly (660.0, 660.1, and 660.R). Each illustrative R-block isthe i^(th) block from each of the flash die, taken together. E.g.,R-block 660.0 is Block 610.65B0 from Flash Die 610.65, block 0 fromFlash Die 610.64 (not explicitly illustrated), and so forth to Block610.1B0 of Flash Die 610.1, and Block 610.0B0 of Hash Die 610.0. Asthere are N blocks per flash die, there are thus a total of N R-blocks(R-block 660.R . . . R-block 660.1, and R-block 660.0).

Another example of an R-block is the i^(th) block and the (i+1)^(th)block from each of the flash die, taken together (e.g. Blocks 610.65B0and 610.65B1 from Flash Die 610.65, blocks 0 and 1 from Flash Die 610.64(not explicitly illustrated), and so forth to Blocks 610.1B0 and 610.1B1from Flash Die 610.1, and Blocks 610.0B0 and 610.0B1 from Flash Die610.0). There are thus N/2 R-blocks, if there are N blocks in each flashdie. Yet another example of an R-block is the i^(th) even and odd blocksfrom each of a plurality of dual plane devices. Other arrangements offlash die blocks for management as R-blocks are contemplated, includingmapping between virtual and physical block addresses to ensure thatR-blocks have one block from each die, even if some blocks areinoperable. In various embodiments, some of the N blocks in each flashdie are used as spares so that the mapping between virtual and physicalblock addresses has spare (otherwise unused) blocks to replace defectiveones of the blocks in the R-blocks.

In various embodiments, reads and/or writes of information in flash dieare performed according to an order, such as a ‘read unit first’ orderor a ‘page first’ order. An example of a read unit first order for readunits illustrated in the figure begins with Read Unit 610.0R0 followedby 610.1R0 . . . 610.65R0, 610.0R1, 610.1R1 . . . 610.65R1, and soforth, ending with 610.65RR. An example of a page first order for readunits illustrated in the FIG. begins with Read Unit 610.0R0 followed by610.0R1 . . . 610.0RR, 610.1R0, 610.1R1 . . . 610.1RR . . . 610.65R0,610.65R1, and so forth, ending with 610.65RR.

In various embodiments, a writing and/or a striping order of data withinan R-block is page (e.g. lowest to highest) first, across all devices(e.g. lowest to highest numbered devices, as suggested conceptually byStriping Direction 600), then the next highest page (across alldevices), and so forth, continuing throughout the last page of theR-block. Specifically with respect to R-block 660.0, an example orderbegins with Page 610.0P0 (the first page in the first block of Flash Die610.0), followed by Page 610.1P0 (the first page in the first block ofFlash Die 610.1), and so forth continuing to Page 610.65P0 (the firstpage in the first block of Flash Die 610.65, and the last block ofR-block 660.0). The example order continues with Page 610.0P1 (thesecond page in the first block of Flash Die 610.0), followed by Page610.1P1 (the second page in the first block of Flash Die 610.1), and soforth continuing to Page 610.65P1 (the second page in the first block ofFlash Die 610.65). The example continues in an identical order. Theexample order completes with Page 610.0PP (the last page in the firstblock of Flash Die 610.0), followed by Page 610.1PP (the last page inthe first block of Flash Die 610.1), and so forth ending with Page610.65PP (the last page in the first block of Flash Die 610.65, and thelast page in the last block of R-block 660.0).

In various embodiments, Flash Die 610.65 . . . 610.1, and 610.0correspond to respective ones of one or more individual Flash Die 194,of FIG. 1A. In some embodiments, Flash Die 610.65 . . . 610.1, and 610.0are a portion less than all of NVM 199. For example, in variousembodiments, data is striped independently across multiple groups offlash die, and each of the groups of flash die is independentlyaccessible.

Higher-Level Redundancy Techniques

FIG. 7 illustrates selected details of various embodiments ofhigher-level redundancy techniques. Flash Device(s) 720 includes 64flash die (Flash Die 610.63, 610.62, 610.61 . . . 610.0 as explicitlyand implicitly illustrated in FIG. 6) and communicates via InterfaceChannel(s) 730. Extra Flash Device(s) 740 includes up to two flash die(Flash Die 610.65 and 610.64 as explicitly and implicitly illustrated inFIG. 6) and communicates via Extra Interface Channel(s) 750. The FlashDie provide storage for higher-level redundancy information and datastorage (e.g. user data and/or user free space) in a storage sub-system,such as NVM in an SSD. (Examples of ‘user data’ in contexts ofredundancy information and data storage include all data other than theredundancy information stored on flash memory for later retrieval, suchas operating system data, application data, SSD management data, and soforth.) Higher-level redundancy enables, e.g., recovering fromintermittent or permanent failure of one or more portions of one or moreflash die, such as a failure to provide error-corrected data (e.g. vialower-level ECC functions) for a read operation or failure to properlycomplete a write operation.

For example, each flash die (or alternatively each block or each pagewithin each block) is operated in a context of a Redundant Array ofSilicon Independent Elements (RASIE). If a failure is detected in aparticular flash die (e.g. due to an ECC-uncorrectable read error of aportion of a block of the particular die), then in response, redundantinformation stored in others of the flash die is used to determineinformation that would have been provided by the particular die. In someembodiments and/or usage scenarios, sufficient redundant information isstored to enable recovery from one failure within one flash die (duringa single operation). Operation in a mode that enables recovery from asingle failure includes, in some embodiments, allocating and managingspace equivalent to one flash die for higher-level redundancyinformation, and is termed ‘RASIE-1’. Operation in a mode that enablesrecovery from two failures includes, in some embodiments, allocating andmanaging space equivalent to two flash die for higher-level redundancyinformation, and is termed ‘RASIE-2’. Operation in a mode that enablesrecovery from three failures includes, in some embodiments, allocatingand managing space equivalent to three flash die for higher-levelredundancy information, and is termed ‘RASIE-3’. RASIE modes such asRASIE-1, RASIE-2, and RASIE-3 are respective examples of non-fractionalRASIE modes, as storage capacity equivalent to an integer multiple ofone or more entire flash die (e.g. one, two, and three entire flash die,respectively) is dedicated to higher-level redundancy information.

In some embodiments and/or usage scenarios, managing die-level failuresis an objective, and spreading information amongst die is performed. Forexample, higher-level redundancy information is stored in one or moredie specifically allocated solely to the higher-level redundancyinformation. In some embodiments and/or usage scenarios, managingblock-level failures is an objective, and spreading information amongstblocks within a die is performed. For example, higher-level redundancyinformation is stored in one or more blocks allocated to thehigher-level redundancy information, the allocation being without regardto which particular die the blocks were part of. In some embodimentsand/or usage scenarios, managing particular-entity-level failuresincludes spreading information so that no more than N elements (e.g. onefor RASIE-1 and two for RASIE-2) are in any one of the particularentities. Example of the entities include a (packaged) device, a die, anR-block, a block, an R-page (described elsewhere herein), a page, cellsassociated with a word line, and one or more pluralities of theforegoing.

The higher-level redundancy information is computed and written inaccordance with (user) data written to the flash die, and is thusavailable to provide information when a failure is detected. In variousembodiments, the higher-level redundancy information is written to theflash die before, after, or in no particular time order with respect towriting of (user) data the higher-level redundancy information isassociated with.

The figure illustrates various embodiments of non-fractional RASIEoperating modes, as summarized in the following table.

Usage Mode Usage of Extra Flash Device(s) 740 Usage of Flash Device(s)720 RASIE-1 1-0 -none- 610.63 (1 die)-redundancy 610.62 . . . 610.0 (63die)-data storage 1-1 610.64 (1 die)-redundancy 610.63 . . . 610.0 (64die)-data storage RASIE-2 2-0 -none- 610.63, 610.62 (2 die)-redundancy610.61 . . . 610.0 (62 die)-data storage 2-1 610.64 (1 die)-redundancy610.63 (1 die)-redundancy 610.62 . . . 610.0 (63 die)-data storage 2-2610.65, 610.64 (2 die)-redundancy 610.63 . . . 610.0 (64 die)-datastorage

More specifically, in (non-fractional) RASIE-1 modes, space equivalentto one die is allocated to higher-level redundancy information. InRASIE-1 mode 1-0, Extra Flash Device(s) 740 is not used, as higher-levelredundancy information is stored in one die of Flash Device(s) 720 (e.g.Flash Die 610.63), leaving 63 of the die (Flash Die 610.62 . . . 610.0)available for data storage (e.g. user data and/or user free space). InRASIE-1 mode 1-1, one die of Extra Flash Device(s) 740 is used (e.g.Flash Die 610.64), leaving all of Flash Device(s) 720 (64 die) availablefor data storage.

In (non-fractional) RASIE-2 modes, space equivalent to two die isallocated to higher-level redundancy information. In RASIE-2 mode 2-0,Extra Flash Device(s) 740 is not used, as higher-level redundancyinformation is stored in two dic of Flash Device(s) 720 (e.g. Flash Die610.63 and Flash Die 610.62), leaving 62 of the die (Flash Die 610.61 .. . 610.0) available for data storage. In RASIE-2 mode 2-1, one die ofExtra Flash Device(s) 740 is used (e.g., Flash Die 610.64), ashigher-level redundancy information is partially stored in one die ofFlash Device(s) 720 (e.g. Flash Die 610.63), leaving 63 of the die(Flash Die 610.62 . . . 610.0) available for data storage. In RASIE-2mode 2-2, two die of Extra Flash Device(s) 740 are used (e.g. Flash Die610.65 and Flash Die 610.64), leaving all of Flash Device(s) 720 (64die) available for data storage.

In some embodiments, die that are unused in all usage scenarios areunpopulated. For example, in a system operable only in RASIE 2-0 modeand RASIE 1-0 mode (but not in other RASIE modes), Extra Flash Device(s)740 is unpopulated.

In some embodiments, higher-level redundancy information is storedentirely in “dedicated” die (e.g. Flash Die 610.63 in RASIE-1 mode 1-0or Flash Die 610.65 and Flash Die 610.64 in RASIE-2 mode 2-2). In otherembodiments, higher-level redundancy information is stored in any of thedie, so for example, in RASIE-1 mode 1-0 Flash Die 610.62 is used forhigher-level redundancy information, while Flash Die 610.63 and FlashDie 610.61 . . . 610.0 are used for data storage. In some embodimentsand/or usage scenarios, higher-level redundancy information is stored indifferent die (and/or portions thereof) over time, so, for example, in afirst time period a first flash die holds higher-level redundancyinformation while in a second time period a second flash die holdhigher-level redundancy information.

In various embodiments, there are a plurality of RASIE 1-0 modes (and aplurality of RASIE 2-0 modes) depending on how many flash die areusable. For example, in a first RASIE 1-0 mode (as illustrated in thetable above), Flash Die 610.63 stores higher-level redundancyinformation, and Flash Dic 610.62 . . . 610.0 are available for datastorage. In a second RASIE 1-0 mode, Flash Die 610.63 is no longerusable, Flash Die 610.62 stores higher-level redundancy information, andFlash Die 610.61 . . . 610.0 are available for data storage, decreasingan available amount of data storage by one die. RASIE modes where a die(or any portions thereof) previously available for data storage is nolonger available for data storage due to use of the die (or theportions) for higher-level redundancy information are sometimes referredto as reduced-capacity RASIE modes.

In some embodiments, higher-level redundancy information is stored usinga same and/or a similar lower-level redundancy and/or error correctioncoding scheme as user data protected by the higher-level redundancyinformation. Using a lower-level redundancy and/or error correctionscheme to protect the higher-level redundancy information enablesdetermining if there is an uncorrectable error in the higher-levelredundancy information, in a same and/or a similar manner that anuncorrectable lower-level error in the user data is determined.

In some embodiments, higher-level redundancy information is stored indifferent die for different portions of data. For instance, in someembodiments where flash die are managed in R-blocks, higher-levelredundancy information is stored in different flash die for differentR-blocks. For example, higher-level redundancy information for anR-block including block 0 of Flash Die 610.0 is stored in Flash Die610.0, while higher-level redundancy information for an R-blockincluding block 1 of Flash Die 610.0 is stored in Flash Die 610.1, andso forth. In some embodiments, such as some embodiments where flash dieare managed in R-blocks, higher-level redundancy information is writtenafter data the higher-level redundancy information depends on is knownand/or is written.

In some usage scenarios, one or more portions of an NVM element (e.g. ablock of a device, such as Block 610.0BB of Flash Die 610.0 of FIG. 6)are, or become during operation, inoperable. In some embodiments, theinoperable portions are mapped out via virtual and physical blockaddresses (e.g. via processing performed via Map 141 and/or Table 143 ofFIG. 1A.). Alternatively, the inoperable portions are skipped (ratherthan explicitly mapped out). In some embodiments based on R-blocks, theskipping results in some of the R-blocks having differing numbers ofblocks. For example, if Block 610.0B0 is defective and unusable, thenR-block 660.0 has one fewer block than R-block 660.1. The higher-levelredundancy information is written in a (per R-block) variable locationthat is, for example, the last block of each R-block.

In various embodiments, one or more elements of FIG. 7 correspond to oneor more elements of FIG. 1A. For example, Flash Device(s) 720 and ExtraFlash Device(s) 740 collectively correspond to NVM 199, and InterfaceChannel(s) 730 and Extra Interface Channel(s) 750 collectivelycorrespond to Device Interfaces 190. For another example, Flash Die610.65 . . . 610.0 collectively correspond to the instances of Flash Die194. For yet another example, one or more of the flash devices of FlashDevice(s) 720 and/or Extra Flash Device(s) correspond to one or more ofthe instances of Flash Devices 192. In various embodiments, one or moreelements of FIG. 1A manage higher-level redundancy information and/orrecover user data based at least in part on the higher-level redundancyinformation in accordance with the RASIE operating modes describedherein. For example, a portion of software execution capabilities of CPU171 is used to manage computation of higher-level redundancy informationaccording to various RASIE operating modes. For another example, DataProcessing 121 and/or ECC-X 135 includes hardware elements dedicated toand/or specialized for computation of higher-level redundancyinformation and/or recovery of user data according to various RASIEoperating modes. For yet another example, ECC 161 detects anECC-uncorrectable (lower-level) read error of a portion of a flash die,and ECC-X 135 detects a RASIE (higher-level) read error and/or enablescorrection thereof.

In various embodiments, Interface Channel(s) 730 variously has one,four, eight, or 16 channels, and Extra Interface Channel(s) 750variously has one or two channels. In various embodiments, FlashDevice(s) 720 is implemented as one, two, four, eight, or 16 devices,each having respectively 64, 32, 16, eight, and four of the Flash Die.In various embodiments, Extra Flash Device(s) 740 is implemented as onedevice having one or two die or as two devices each having one die. Insome embodiments, the Flash Die of Extra Flash Device(s) 740 areimplemented in devices that also implement the Flash Die of FlashDevice(s) 720. For example, one flash device implements 66 flash die(Flash Die 610.65 . . . 610.0). For another example, two flash deviceseach implement 33 flash die, e.g. in a first flash device (Flash Die610.65 . . . 610.33) and in a second flash device (Flash Die 61032 . . .610.0). Other arrangements of flash die and flash devices arecontemplated. In some embodiments having Extra Flash Device(s) 740implemented in devices that also implement flash die of Flash Device(s)720, the flash die communicate via shared interface channels, oralternatively via interface channels dedicated to particular ones (orsets) of the flash die. While Flash Device(s) and Extra Flash Device(s)740 are illustrated with specific numbers of flash die (2 and 64,respectively), other embodiments are contemplated, such as FlashDevice(s) 720 having 2, 4, 8, 16, 32, or 128 flash die, and/or ExtraFlash Device(s) 740 having 0, 1, or 4 flash die.

FIG. 8 illustrates selected details of an embodiment of dynamichigher-level redundancy mode management with RASIE, such as dynamicallyswitching between RASIE modes enabled by the various embodimentsillustrated by FIG. 6 and/or FIG. 7. In some embodiments and/or usagescenarios, a form of graceful degradation is provided where a storagesub-system (e.g. an SSD) is dynamically transitioned from operating infirst higher-level redundancy mode to operating in a second higher-levelredundancy mode. The transition is in response to detection of afailure, such as a permanent or intermittent malfunction of an entireflash die or one or more portions thereof, or an operation (such as aread or write operation) thereto. According to various embodiments, thetransition is one or more of: global for the SSD; performed on one ormore subsets of the SSD; and performed on one or more R-blocks, blocks,and/or pages of the SSD. For example, if a particular block of one ofthe NVM devices storing RASIE-2 information fails during programming,then subsequent operation of the R-block containing the particular(failed) block transitions to a different higher-level redundancy mode(e.g. a RASIE-1 mode), whereas other R-blocks in the SSD are unaffectedand continue to operate in the RASIE-2 mode.

With respect to FIG. 8, processing begins with higher-level redundancyinformation and data storage (e.g. user data and/or user free space)arranged in flash die in accordance with a first higher-level redundancymode (Operate in First Higher-Level Redundancy Mode 802). Flow thenproceeds to determine if a failure has been detected (Failure? 803),such as a lower-level uncorrectable read error or a write/programfailure. If no failure has been detected, then flow proceeds back tocontinue operation in the first higher-level redundancy mode. If afailure has been detected, then flow proceeds to switch from operatingin the first higher-level redundancy mode to operating in a secondhigher-level redundancy mode (Dynamically Transition Operating Mode809).

The switch begins by (optionally) decreasing space available for datastorage (Reduce Free Space 804) to account for the failure. If thesecond higher-level redundancy mode uses sufficiently less higher-levelredundancy information than the first higher-level redundancy mode, thenthe decreasing of available space is omitted. The switch continues byreorganizing data storage in accordance with the second higher-levelredundancy mode (Rearrange Data Storage 805). The reorganizing includesoptionally moving all user data and/or user free space from the flashdie where the failure occurred to another one of the flash die (userfree space movement is accomplished, in some embodiments, bymanipulation of pointers and/or other data structure elements). Theswitch further continues by selectively restoring (if possible), via thehigher-level redundancy information of the first higher-level redundancymode, any user data that was stored in the flash die where the failureoccurred, and writing the restored user data to another one of the flashdic, in accordance with the second higher-level redundancy mode(Recover/Store Failed User Data 806). The restoring is omitted if thefailure is a write/program failure. The switch further continues byoptionally computing and writing to the flash die higher-levelredundancy information in accordance with the second higher-levelredundancy mode (Determine/Store Revised Higher-Level RedundancyInformation 807). The computing and the writing are omitted if thesecond higher-level redundancy mode is operable with higher-levelredundancy information that was previously in place due to operating inthe first higher-level redundancy mode. Then operation begins in thesecond higher-level redundancy mode (Operate in Second Higher-LevelRedundancy Mode 808).

The failure detection (Failure? 803) is via one or more of: lower-levelredundancy and/or error correction (e.g. in accordance with one or moreECC techniques), higher-level redundancy and/or error correction (e.g.in accordance with one or more RASIE techniques), and failing statusreported by one or more of the flash die or portions thereof. Forexample, more than a threshold number of lower-level error correctionsof reads within a particular portion (e.g. R-block, block, R-page, page,read unit, or cells associated with a word line) of a particular flashdie optionally and/or conditionally results in the particular flash die(or the particular portion) being treated as failed and a higher-levelredundancy mode switch is performed so that the failed flash die (orportion) is no longer used. For another example, if a higher-level errorcorrection fails, then an appropriate one of the flash die (or portionthereof) is treated as failed and a higher-level redundancy mode switchis performed so that the failed flash die (or portion) is no longerused. For yet another example, if a flash die returns a program failurestatus (indicating that a write operation was unsuccessful), then anappropriate block of an appropriate one of the flash die is treated asfailed, and optionally and/or conditionally a higher-level redundancymode switch is performed so that the failed flash die (or alternativelya portion thereof) is no longer used.

In some embodiments, a failed block is replaced by remapping via virtualand physical block addresses (e.g. via processing performed via Map 141and/or Table 143 of FIG. 1A). A spare block from a pool of spare blocksis mapped in place of the failed block. Any contents written in thefailed block are copied to the replacement block, and writing proceedsin the spare block from where the failure occurred in the failed block.

In some embodiments, a failed block is skipped (rather than explicitlyremapped), resulting in a “hole” that optionally and/or conditionallyresults in a higher-level redundancy mode switch when the R-block thatthe hole is in is next erased (in preparation for re-writing). If thehole is in a location for data storage, then no switch is made, and thehole remains. If the hole is in a location for higher-level redundancyinformation, then the higher-level redundancy information is stored inanother location, and optionally the higher-level redundancy mode isswitched.

In some embodiments and/or usage scenarios, restoration of user datastored in the flash die where the failure occurred is not possible. Forexample, if the failure is due to some types of failures detected viahigher-level redundancy and/or error correction and/or some types offailing status reported by one or more of the flash die or portionsthereof, then some user data is lost.

In some embodiments, processing of FIG. 8 is performed in a context of(e.g. an SSD controller) dynamically transitioning between higher-levelredundancy modes in response to a plurality of failures. Specifically,the SSD controller begins operating in a first higher-level redundancymode and dynamically transitions to a second higher-level redundancymode in response to a first failure, and subsequently dynamicallytransitions from the second higher-level redundancy mode to a thirdhigher-level redundancy mode in response to a second failure, and soforth. For instance, an SSD controller operates various flash die inaccordance with a RASIE-2 mode 2-2 and dynamically transitions theoperation to be in accordance with a RASIE-2 mode 2-1 in response to afirst failure. Subsequently, the SSD controller dynamically transitionsthe operation to be in accordance with a RASIE-2 mode 2-0 in response toa second failure. Further subsequently, the SSD controller dynamicallytransitions the operation to be in accordance with a RASIE-1reduced-capacity mode 1-0 in response to a third failure (thereduced-capacity mode 1-0 being similar to RASIE-1 mode 1-0 except withone flash die used for higher-level redundancy information and 62 flashdie used for data storage).

As a specific example, consider an SSD controller (such as SSDController 100 of FIG. 1A) coupled to the elements of FIG. 7, initiallyoperating in RASIE-2 mode 2-2 (e.g. higher-level redundancy informationin Flash Die 610.65 and Flash Die 610.64, and data storage in Flash Die610.63 . . . 610.0), corresponding to operating in the firsthigher-level redundancy mode. Then a read, or alternatively a write, ofone or more of the Flash Die is performed. The read results in anuncorrectable (lower-level) ECC failure, or alternatively the write isunsuccessful, in a portion of a particular one of the Flash Die (e.g. apage of Flash Die 610.62 used for user data and/or user free space). Inresponse, the SSD controller dynamically switches from operating inRASIE-2 mode 2-2 to RASIE-2 mode 2-1, no longer using any of Flash Die610.62. As operation in RASIE-2 mode 2-1 provides 63 die for datastorage (versus 64 die in RASIE-2 mode 2-2), space available for datastorage is decreased from 64 dic to 63 dic, and user data and/or userfree space is moved accordingly. E.g., all user data from Flash Die610.62 is moved to portions of Flash Die 610.63 and Flash Die 610.61 . .. 610.0 in accordance with user free space. Any user data in the pagehaving the uncorrectable ECC failure is recovered based on thehigher-level redundancy information in Flash Die 610.65 and/or Flash Die610.64. Higher-level redundancy information based on data storage inFlash Die 610.63 and Flash Die 610.61 . . . 610.0 and in accordance withRASIE-2 mode 2-1 is computed and stored in Flash Die 610.65 and/or FlashDie 610.64. The SSD controller then operates in RASIE-2 mode 2-1(higher-level redundancy information in Flash Die 610.65 and Flash Die610.64, and data storage in Flash Die 610.63 and Flash Die 610.61 . . .610.0).

While the foregoing described several embodiments of dynamichigher-level redundancy mode management with independent siliconelements of a quantum of an entire flash die, other embodimentsimplement dynamic higher-level redundancy mode management withindependent silicon elements that are portions of a die, such as afraction of an entire flash die (e.g. one-half or one-fourth of a flashdie), one or more read units, word line associated cells, pages,R-pages, blocks, or R-blocks.

In various embodiments, processing of or relating to one or moreelements of FIG. 8 is performed entirely or in part by one or moreelements (or portions thereof) of FIG. 1A. For example, a portion ofsoftware execution capabilities of CPU 171 is used to manage dynamictransitioning between higher-level redundancy modes, such as bydirecting decreasing space available for data storage or directingreorganizing data storage. For another example, Data Processing 121and/or ECC-X 135 includes hardware elements dedicated to and/orspecialized for computation of higher-level redundancy information inaccordance with a ‘target’ redundancy mode. For yet another example, ECC161 implements lower-level (e.g. ECC) error correction and detection ofuncorrectable errors, while ECC-X 135 implements higher-level (e.g.RASIE) error correction and detection of uncorrectable errors and/ormemory element failures. For another example, all or any portions offunctionality relating to dynamic transitioning between (higher-level)redundancy modes is performed by one or more portions of ECC-X 135.

Higher-Level Redundancy and Adaptive Lower-Level Code Rates

In some embodiments and/or usage scenarios, lower-level redundancyand/or error correction uses an adaptive code rate (e.g. an adaptive ECCtechnique using a variable code rate). For instance, a first read unitis managed with a first code rate that provides relatively more usabledata bits than a second read unit that is managed with a second coderate. In some embodiments and/or usage scenarios with lower-levelredundancy and/or error correction using a variable code rate,higher-level redundancy information is stored in portions of independentsilicon elements (such as portions of flash die) that are managed withlower-level redundancy and/or error correction that provides relativelymore usable data bits or the most usable data bits with respect to datastorage protected by the higher-level redundancy information. Theportion(s) where the higher-level redundancy information is storedvaries, in various embodiments and/or usage scenarios, on a per R-blockbasis, on a per-die basis, dynamically over time, or any combinationthereof. In various embodiments, one or more die, R-blocks, blocks,and/or pages are selected for storage of higher-level redundancy databased on having the most usable data with respect to lower-level errorcorrection code rate.

For example, higher-level redundancy information is stored at varyinglocations (such as block locations) on a per R-block basis, thelocations (such as blocks) being those having the most usable data basedon lower-level error correction code rate. In an arbitrary example,consider a RASIE-2 operating mode scenario in the context of FIG. 7,wherein the collection of 66 flash die is treated as a logical “stack”of up to M R-blocks of one-block height each, where M is the number ofblocks per flash die. (In the most conceptually straightforward case,each R-block in the stack is made up of the same physical block numberfrom each die, but to accommodate failed blocks this constraint islifted in at least some embodiments. In yet other embodiments, theconstraint is maintained, but “holes” are accommodated corresponding tothe failed blocks.) Thus, each R-block has up to 66 blocks,corresponding to one block from each of Flash Die 610.0 through FlashDie 610.65. (In FIG. 7, while only some flash die in the range 610.0through 610.65 are explicitly enumerated, it is understood by the use ofellipsis that all flash die in this range are implicitly illustrated.)The higher-level redundancy information is written into whichever blocksof each R-block have the most useable data based on lower-level errorcorrection code rate. If for example in a first R-block, blockscorresponding to Flash Die 610.15 and 610.49 happen to have the mostusable data based on lower-level error correction code rate, thenhigher-level redundancy information is written into those blocks(corresponding to Flash Die 610.15 and 610.49). While if in a secondR-block, blocks corresponding to Flash Die 610.9 and 610.35 happen tohave the most usable data based on lower-level error correction coderate, then higher-level redundancy information is written into thoseblocks (corresponding to Flash Die 610.9 and 610.35). In someembodiments, the higher-level redundancy data is written after all otherdata in an R-block is known.

FIG. 9 illustrates an embodiment of Rcad Units (911, 931 . . . 951, 971)having lower-level redundancy information of adaptive (e.g. differingand/or varying over time and/or by location) code rates protected byhigher-level redundancy information stored in one or more of the readunits. Each of the read units has a portion enabled and/or allocated tocontain User Data (911.U, 931.U . . . 951.U, 971.U), and a remainingportion enabled and/or allocated to contain lower-level redundancyinformation, such as check bits of an ECC code as Lower-Level ECC(911.E, 931.E . . . 951.E, 971.E).

In the figure, vertical dimensions are relatively to scale andindicative of relative size. Thus Read Units 911 and 951 are of a samefirst size (in some embodiments, all read units are a same size for allblocks of all NVM devices), Lower-Level ECC portions 931.E and 951.E areof a same second size, and Lower-Level ECC portions 911.E and 971.E areof a same third size. Read Unit 931 is larger than Read Units 911 and951 that are in turn larger than Read Unit 971. User Data portion 931.Uis larger than User Data portion 951.U. User Data portion 951.U islarger than User Data portion 911.U. Lower-Level ECC portion 951.E issmaller than Lower-Level ECC portion 911.E.

As illustrated in the figure, respective read units have respectivesizes, e.g. per respective block of NVM, enabling varying lower-levelcode rates as used in the respective blocks. More specifically, ReadUnits 931 and 951 have a same amount of lower-level redundancyinformation (931.E and 951.E are a same size), but a lower-level coderate of Read Unit 931 is higher than a lower-level code rate of ReadUnit 951, as Read Unit 931 contains more User Data (931.U) than ReadUnit 951 (containing User Data 951.U).

As illustrated in the figure, respective read units have respectivesizes of user data, enabling various sizes of user data in each of twoor more read units of a same size. For example, a size of user data isvaried to change a lower-level code rate used in a particular read unit.More specifically, Read Units 951 and 911 have a same size, but havedifferent respective amounts of User Data (951.U and 911.U), and thusdifferent respective amounts of lower-level redundancy information(951.E and 911.E), enabling Read Unit 951 to have a higher lower-levelcode rate than Read Unit 911.

In some embodiments and/or usage scenarios, varying and/or changing alower-level code rate advantageously enables providing a sufficientamount of lower-level ECC information to achieve lower-level errorcorrection requirements while maximizing an amount of user data.

In some embodiments with a varying amount of user data in read units,higher-level redundancy information is stored in a one or more of theread units having a largest amount of user data. For example in FIG. 9,using a RASIE-1 mode, higher-level redundancy information is stored inUser Data 931.U, and using a RASIE-2 mode, higher-level redundancyinformation is stored in User Data 931.U and User Data 951.U. Storingthe higher-level redundancy information in read units with the largestamount of user data (among the read units protected by the higher-levelredundancy information) ensures that there is sufficient higher-levelredundancy information to protect the user data in all of the other readunits.

According to various embodiments, one or more techniques are used todetermine which of one or more read units among a number of read unitsprotected by higher-level redundancy information are used to storehigher-level redundancy information. In a first example, thelatest-written one (for RASIE-1) or two (for RASIE-2) read units thathave a largest amount of user data are used. In a second example, theearliest-written one (for RASIE-1) or two (for RASIE-2) read units thathave a largest amount of user data are used. Similarly, any technique todeterministically select one or more read units having a largest amountof user data so as to protect all of the remaining user data in theother read units is within the scope of the techniques consideredherein.

Higher-Level Redundancy Information Computation Techniques

In various embodiments and/or usage scenarios, higher-level redundancyinformation is computed with a variety of techniques, such as viaparity, RS, and/or weighted-sum techniques. For example, in somehigher-level redundancy modes enabling recovery from one (lower-level)failure (e.g. RASIE-1), higher-level redundancy information is computedvia parity techniques. For another example, in some higher-levelredundancy modes enabling recovery from two (lower-level) failures (e.g.RASIE-2), higher-level redundancy information is computed via acombination of parity and RS techniques. A first portion of thehigher-level redundancy information is computed using parity coding anda second portion is computing using RS coding. For yet another example,in some higher-level redundancy modes enabling recovery from twofailures (e.g. RASIE-2), higher-level redundancy information is computedvia a combination of parity and weighted-sum techniques. A first portionof the higher-level redundancy information is computed using paritycoding and a second portion is computing using weighted-sum coding. Thehigher-level redundancy information is managed, e.g. via reads andwrites of pages of NVM, using lower-level failure detection techniques(such as ECC) identical to or similar to lower-level failure detectiontechniques used for pages of the NVM available for storing dataprotected by the higher-level redundancy information.

As a specific example for RASIE-2, a first page of higher-levelredundancy information is computed using parity coding via an XOR of allfirst pages in a stripe across an R-block. More specifically, an XOR isperformed of all of the first bytes of all of the first pages in thestripe across the R-block, resulting in a first byte of the first pageof higher-level redundancy information. Similarly, a second byte ofhigher-level redundancy information is formed by XORing all of thesecond bytes of all of the first pages in the stripe across the R-block,and so forth for all of the bytes of all of the first pages in thestripe. A second page of higher-level redundancy information is computedusing a weighted-sum technique as follows.

Arithmetic is performed over a finite field, such as a Galois Field(used as an example). Examples assume data being operated on isbyte-wide, and thus a field such as GF(256) is used. In variousembodiments, data is operated on in any units.

Each page in a stripe is assigned a unique non-zero “index”. The valuesof the indices are chosen to simplify implementation complexity, and arenot related to any form of generator polynomial. For example, the pagesare labeled (e.g. by software) by die location in a stripe from 0 toN−1, and a suitable value for the indices is the ones-complement of thedie number (ensured to be non-zero provided N<255). Another selection ofindex values is the lowest-weight (fewest number of set bits or fewestnumber of clear bits) non-zero integers, e.g. to reduce and/or minimizehardware costs. Selecting gray-coded values for the indices, in someembodiments and/or usage scenarios, minimizes transitions and/or reducespower as pages are processed.

The index values are not selected according to finite field arithmetic,but are selected according to other principles. Notwithstanding this,each index value corresponds to a non-zero element in the finite field.Assume that page i has index value Ki (and page j has index value Kj).The weighted-sum redundancy is the (GF field) sum (over correspondingbytes Pi from each page i) of Ki*Pi, each byte multiplied (over the GFfield) by its index value.

Thus weighted-sum redundancy information is computed for each byte as:

-   -   R0=sum over all corresponding bytes Pi;    -   R1=sum over all corresponding bytes Ki*Pi;    -   R0 is the XOR of all the corresponding bytes; and    -   R1 is a weighted sum of the bytes, where the weights are        selected as the index values. The foregoing computation is        iterated for each of the corresponding bytes in a page,        producing corresponding pages of bytes for each of R0 and R1. In        the following discussion, R0 and R1 are described in some        contexts respectively as single elements (e.g. each being a        single byte) for clarity of exposition, but as in the foregoing        computation, each are representative of a respective page of        elements (e.g. each being a page of bytes).

Pi represents a byte in page i, and Pj represents a byte in page j.Processing is described with respect to one stripe of correspondingbytes from each page, and iteration is performed over all correspondingbytes. If some pages are “shorter” than others, due to for example tohaving a different (lower-level) redundancy code rate, then the shorterpages are zero-padded (or padded by any known value used the same way onencode and decode) so that all pages that are processed effectively havethe same size.

Summations to compute R0 and R1 are performable in any order, viavarious serial and/or parallel computations, according to variousembodiments. Pages do not have to be processed in any specific order aswhether Ki*Pi is added in prior to or subsequent to Kj*Pj has no effecton the result in R1. Computation of R0 and R1 values corresponding tovarious bytes of a page of redundancy information are independent ofeach other and are computable in any order, via various serial and/orparallel computations, according to various embodiments. Further,subtracting Ki*Pi from R1 (and subtracting Pi from R0) enables “backingout” of computation effects on pages. Since over a GF field, additionand subtraction are both XOR (thus subtracting is equivalent to simplyadding in a second time), in some embodiments and/or usage scenarios, nospecial hardware is needed for GF field implementations (e.g. a logicalXOR capability is sufficient) to “back out” a page.

In the event of an uncorrectable lower-level error, higher-level errorcorrection begins, in some embodiments, by re-computing R0 and R1, butby omitting page(s) (sometimes referred to as column(s)) that haveuncorrectable lower-level errors. Correction proceeds by subtracting therecomputed R0 from the original R0 to produce ΔR0, and subtracting therecomputed R1 from the original R1 to produce ΔR1.

If there are no uncorrectable lower-level errors, then the recomputed R0and R1 are both zero. If there are uncorrectable lower-level errors,then the recomputed R0 and R1 (after the subtraction) reflect the“missing” data (that was not added in the second time, but was presentin the original values).

If there is one uncorrectable lower-level error, then the recomputed R0is used to correct the error (and the recomputed R1 is not needed).

If there are two uncorrectable lower-level errors, then the recomputedR0 and R1 are used to correct the errors. If both the pages of R0 and R1values are the pages with uncorrectable lower-level errors, then nocorrection of data storage pages is needed. If the page of R1 values isone of the pages with uncorrectable lower-level errors, then correctionis via R0 (the recomputed R0 value is the value of the data storage pagewith uncorrectable lower-level errors).

If there are two uncorrectable lower-level errors in data storage pages,or if the R0 page is one of the pages with uncorrectable lower-levelerrors, then correction starts by computing ΔR0 and ΔR1 as above. If theR0 page is one of the pages with uncorrectable lower-level errors,computation of the ΔR0 page is optionally omitted. If page i and page jare pages with uncorrectable lower-level errors, then the recomputedΔR0=Pi+Pj, and the recomputed ΔR1=Ki*Pi+Kj*Pj. Equation solvingproduces:

Pi=(ΔR1−Kj*ΔR0)/(Ki−Kj)

Pj=ΔR0−Pi

If R0 is one of the pages with uncorrectable lower-level errors, then(because R0 is not included in R1), ΔR1=Ki*Pi, or Pi=ΔR1/Ki; the sameresult obtained by setting Kj=0 in the formulas above (to ignore ΔR0).

In an alternative embodiment, a finite field defined by integers mod p,where p is a prime, is used instead of a Galois Field. The computationsare identical to those described above, with addition being integeraddition mod p, and multiplication being integer multiplication mod p.For example, if pages are pages of bytes, a finite field of integers mod257 is used. All user data bytes are in a range 0-255 and are stored inone byte each. R1 results, however, have values ranging from 0-256,requiring more than one byte for representation. There are many ways toencode values from 0-256 to minimize storage space and enable the R1page to be stored with reduced overhead. For example, values 0 and 256are stored as nine-bit sequences 000000000 and 000000001 respectively,and all other values are stored in eight bits. Given a randomdistribution of R1 values, storage overhead is <0.1%. As described withrespect to FIG. 9, the R1 page is selected to have a largest amount ofuser data, enabling the storage overhead to be hidden in some usagescenarios.

FIG. 10 illustrates selected details of an embodiment of higher-levelredundancy information result and data source correspondences, forinstance as used by RASIE-2 mode 2-2 in a context such as FIG. 7 and asfurther illustrated in FIG. 6. FIG. 10 explicitly illustrates Flash Die610.0, 610.63, 610.64 and, 610.65, and by ellipsis ( . . . ) implicitlyillustrates Flash Die 610.1 . . . 610.62. Selected details of blocks,pages, and bytes within pages of the Flash Die are illustrated. A firstportion of higher-level redundancy information is illustrated as R0 1010(stored in Flash Die 610.64), and is computed using parity coding. Asecond portion of higher-level redundancy information is illustrated asR1 1011 (stored in Flash Die 610.65), and is computed using weighted-sumcoding. Storage for data information is illustrated as Data 1019 (storedin Flash Die 610.0 . . . 610.63).

Dashed-arrow 1001 conceptually indicates a two-byte redundancycomputation result (one byte for each of R0 1010 and R1 1011) based oncorresponding first bytes of all first pages (across all flash die) ofData 1019. As illustrated, the two-byte result is the first byte on eachof the first R0 and R1 pages. Dashed arrow 1002 conceptually indicates atwo-byte redundancy computation result (one byte for each of R0 1010 andR1 1011) based on corresponding last bytes of all first pages of Data1019. As illustrated, the two-byte result is the last byte on each ofthe first R0 and R1 pages. Dashed-arrow 1003 conceptually indicates atwo-page redundancy computation result (one page for each of R0 1010 andR1 1011) based on corresponding last pages of the first blocks (acrossall flash die) of Data 1019.

Note that as described elsewhere herein, in some embodimentshigher-level redundancy information is stored in different die fordifferent portions of data. Thus, R0 and R1, in some embodiments, arestored across various die, rather than two “dedicated” die, asillustrated in FIG. 10.

FIG. 11 illustrates selected details of an embodiment of higher-levelredundancy information computations, for instance as used by RASIE-2mode 2-2 in a context such as FIG. 7 and as further illustrated in FIG.6 and FIG. 10, with various operating conditions according to variousembodiments. More specifically. FIG. 11 illustrates parity codingcomputation for a byte of R0 and weighted-sum coding computation for abyte of R1, in accordance with, e.g., the two-byte redundancycomputation result illustrated conceptually by dashed-arrow 1001 of FIG.10. The operating conditions include one or more of: performingarithmetic over a finite field (such as a Galois Field), indices(corresponding to dummy summation variable “i” values in FIG. 11) beingones-complement of flash die number (or any other unique and non-zeronumbering), and indices corresponding to non-zero elements in the finitefield. The computation as illustrated in FIG. 11 is repeated for all ofthe bytes of R0 and R1, based on the corresponding data bytes. Note thatnon-zero indices enable R1 values to include a contribution from everyelement of Pi.

Thus there are no dependencies on computing any of the bytes of R0 oneach other or between any of the bytes of R1. Therefore variousembodiments are contemplated where R0 and R1 values are computedentirely (massively) in parallel, partially in parallel, or entirely inserial. For example, all of the R0 and/or R1 bytes of a page arecomputed in parallel. For another example, all of the R0 bytes of a pageare computed in parallel followed (or preceded) by computing in parallelall of the R1 bytes of a page.

Further, there are no ordering requirements on computing any of thebytes of R0 with respect to each other or with respect to computing anyof the bytes of R1. Therefore various embodiments are contemplated whereR0 and R1 values are computed entirely in-order with respect to eachother, in-order with respect to each other separately (e.g. R0computations are in-order with respect to each other but with noordering with respect to R1, and vice-versa), or with no particularordering (e.g. entirely out-of-order, unordered, or randomly ordered).For example, all of the R0 bytes of a page are computed in a particularorder (e.g. from lowest byte to highest byte), followed by all of the R1bytes of the page in the particular order. For another example, all ofthe R0 bytes of a page are computed in the particular order, andindependently all of the R1 bytes of the page are computed in theparticular order. For yet another example, all of the R0 bytes of a pageas well as all of the R1 bytes of a page are computed in no particularorder with respect to each other (e.g. as data operands becomeavailable).

For yet another example, all of the R0 and R1 bytes of one or more pagesare computed in an order determined by an order of completion of one ormore read operations performed on one or more NVMs (each having, e.g.,one or more flash die), the read operations for reading the data bytesreferenced by the summation and weighted-summation computations (Pi)illustrated in FIG. 11. Performing the computations in the orderdetermined by the completion of the read operations enables, in someembodiments and/or usage scenarios, reduction or elimination ofbuffering between the NVMs and elements enabled to perform thecomputations. Performing the computations in the order determined by thecompletion of the read operations enables, in some embodiments and/orusage scenarios, reduction in memory bandwidth used to perform thecomputations, such as memory bandwidth of the NVMs.

For yet another example, all of the R0 and R1 bytes of one or more pagesare computed in an order determined by an order of data returned and/ordata available in response to read operations performed on one or moreNVMs (each having, e.g., one or more flash die), the data returnedand/or data available corresponding to the data bytes referenced by thesummation and weighted-summation computations (Pi) illustrated in FIG.11. In some embodiments and/or usage scenarios, performing thecomputations in the order determined by the data returned and/or dataavailable reduces or eliminates buffering between the NVMs and elementsenabled to perform the computations. In some embodiments and/or usagescenarios, performing the computations in the order determined by thedata returned and/or data available reduces memory bandwidth used toperform the computations, such as memory bandwidth of the NVMs. In someembodiments, the read operations are performed in a particular order(e.g. from lowest byte to highest byte of Pi), while in otherembodiments, the read operations are performed in no particular order.

FIG. 12 illustrates selected details of an embodiment of recovery fromone (lower-level) failure (during a single operation), for instance in acontext such as associated with FIG. 11, and where the lower-levelfailure has occurred on page j. Note that if the lower-level failure ison an R0 or an R1 page, then R0 (or R1) is re-determined as described byFIG. 11. FIG. illustrates a computation for one byte of a recoveredvalue for page j (note that the summation omits page j where the failureoccurred). The computation as illustrated in FIG. 12 is repeated todetermine recovered values for all of the bytes of page j, based oncorresponding bytes of R0 and corresponding bytes from all of the datapages except for page j.

Thus there are no dependencies on computing any of the bytes of therecovered values of page j on each other. Therefore various embodimentsare contemplated where Pj recovery values are computed ranging fromhighly parallel to highly serial, similarly to the aforementionedcomputations for R0 and R1 values. Further, there are no orderrequirements on computing any of the recovery values of page j withrespect to each other. Therefore various embodiments are contemplatedwhere Pj recovery values are computed in varying orderings with respectto each other, similarly to the aforementioned computations for R0 andR1 values.

Some exemplary embodiments perform computations related to determiningrecovery values in orderings at least in part determined by an orderingof completion of one or more read operations performed on one or moreNVMs (each having, e.g., one or more flash die), the read operations forreading the NVMs to obtain R0 and/or Pi values as illustrated by FIG.12. Performing the computations in the order of the completion of theread operations enables, in some embodiments and/or usage scenarios,reduction or elimination of buffering between the NVMs and elementsenabled to perform the computations. Performing the computations in theorder of the completion of the read operations enables, in someembodiments and/or usage scenarios, reduction in memory bandwidth usedto perform the computations, such as memory bandwidth of the NVMs.

Some exemplary embodiments perform computations related to determiningrecovery values in orderings at least in part determined by an orderingof data returned and/or data available from one or more NVMs (eachhaving, e.g., one or more flash die), the data returned and/or dataavailable being in response to read operations performed on the NVMs toobtain R0 and/or Pi values as illustrated by FIG. 12. In someembodiments and/or usage scenarios, performing the computations in theorder of the data returned and/or data available from the readoperations reduces or eliminates buffering between the NVMs and elementsenabled to perform the computations. In some embodiments and/or usagescenarios, performing the computations in the order of the data returnedand/or data available from the read operations reduces memory bandwidthused to perform the computations, such as memory bandwidth of the NVMs.In some embodiments, the read operations are performed in a particularorder (e.g. from lowest byte to highest byte of Pi), while in otherembodiments, the read operations are performed in no particular order.

FIGS. 13A-13D illustrate selected details of an embodiment of recoveryfrom two (lower-level) failures (during a single operation), forinstance in a context such as associated with FIG. 11, and where thelower-level failures have occurred on pages m and n. Note that if thelower-level failures are on R0 and R1 pages, then R0 and R1 are unneededfor data recovery, and there is no processing to recover data.Otherwise, note that if one of the lower-level failures is an R1 page,then data recovery proceeds as described by FIG. 12. If neither of thelower-level failures are on R0 or R1 pages, then recovery of Pm and Pnvalues proceeds as follows. FIG. 13A illustrates computations for onebyte of a revised R0 as R0′ and for one byte of a revised R as R1′ (notethat the summations omit pages m and n where the failures occurred).FIG. 13B illustrates equalities relating one byte of the originalredundancy information (R0, R1) to the revised redundancy information(R0′, R1′), and the terms omitted from the summations used to form therevised R0 and R1 (Pm+Pn and Km*Pm+Kn*Pn). FIG. 13C illustrates analgebraic rearrangement of FIG. 13B, with introduced terms delta R0(ΔR0) and delta R1 (ΔR1). FIG. 13D illustrates a solution of FIG. 13Cfor Pn and Pm, and thus represents computations for one byte of arecovered value for page n and one byte of a recovered value for page m,based on the corresponding bytes of R1, R0, and corresponding bytes fromall of the data pages except for pages m and n. Note that unique indicesenable a non-zero denominator, as Kn is unique with respect to Km.

In various embodiments, computations as represented by FIGS. 13A-13D areperformed to determine one byte of a recovered value for page m and onebyte of a recovered value for page n. The computations are repeated todetermine recovered values for all of the bytes of pages m and n, basedon corresponding bytes of R0, R1, and corresponding bytes from all ofthe data pages except for pages m and n.

Thus there are no dependencies on computing any of the bytes of therecovered values of pages m or n on each other. Therefore variousembodiments are contemplated where Pm and/or Pn recovery values arecomputed ranging from highly parallel to highly serial, similarly to theaforementioned computations for Pj recovery values. Further, there areno order requirements on computing any of the recovery values of page mand/or page n with respect to each other. Therefore various embodimentsare contemplated where Pm and/or Pn recovery values are computed invarying orderings with respect to each other, similarly to theaforementioned computations for Pj recovery values.

Some exemplary embodiments perform computations related to determiningrecovery values (such as computations for R0′ and R1′) in orderings atleast in part determined by an ordering of completion of one or moreread operations performed on one or more NVMs (each having, e.g., one ormore flash die), the read operations to obtain any one or more of valuesillustrated as sources for computations in any of FIGS. 13A-13D.Performing the computations in the order of the completion of the readoperations enables, in some embodiments and/or usage scenarios,reduction or elimination of buffering between the NVMs and elementsenabled to perform the computations. Performing the computations in theorder of the completion of the read operations enables, in someembodiments and/or usage scenarios, reduction in memory bandwidth usedto perform the computations, such as memory bandwidth of the NVMs.

Some other exemplary embodiments perform computations related todetermining recovery values (such as computations for R0′ and R1′) inorderings at least in part determined by an ordering of data returnedand/or data available from one or more NVMs (each having, e.g., one ormore flash die), the data returned and/or data available being inresponse to read operations performed on the NVMs to obtain any one ormore of values illustrated as sources for computations in any of FIGS.13A-13D. In some embodiments and/or usage scenarios, performing thecomputations in the order of the data returned and/or data availablefrom the read operations reduces or eliminates buffering between theNVMs and elements enabled to perform the computations. In someembodiments and/or usage scenarios, performing the computations in theorder of the data returned and/or data available from the readoperations reduces memory bandwidth used to perform the computations,such as memory bandwidth of the NVMs. In some embodiments, the readoperations are performed in a particular order (e.g. from lowest byte tohighest byte of Pi), while in other embodiments, the read operations areperformed in no particular order.

FIGS. 14A and 14B illustrate selected details of an embodiment ofcomputing higher-level redundancy information with respect to pagesreceived from NVMs. FIG. 14A illustrates selected details of anembodiment of sending a plurality of read commands to one or more NVMsvia issuing (Issue Read Operation 1402A), checking if all of thecommands have been sent (All Issued? 1403A), and if not, then loopingback to send another of the commands. Note that other embodiments arecontemplated where a plurality of commands are issued at a time, ratherthan one at a time.

FIG. 14B illustrates selected details of an embodiment of processingpages received from the NVMs in response to the read commands sent asillustrated in FIG. 14A. A check is made to determine if a page isavailable (Page Ready? 1402B). If not, then processing loops back toperform the check again. If a page is available, then higher-levelredundancy information processing relating to the page is carried out(Perform Page-Based Computations 1403B). Then a check is made todetermine if all pages have been processed (Pages Finished?1404B). Ifso, then processing is complete (End 1499B), otherwise flow loops backto determine if another page is available.

Other than reception of pages in response to the commands sent asillustrated in FIG. 14A, the processing illustrated in FIG. 14B isindependent of processing illustrated in FIG. 14A. In various scenarios,arrival order of the pages varies according to the NVM type, state,operating environment, and other factors, and in some circumstances isdifferent than sending order or arrival order of the read commandscorresponding to the arriving pages. As processing of FIG. 14A isindependent of FIG. 14B (other than page data arrival being dependent ona corresponding read command being sent), in some embodiments and/orusage scenarios, read commands are being sent (FIG. 14A) while read datais being received/processed (FIG. 14B). In some embodiments and/or usagescenarios, some of the pages are provided from one or more buffersrather than being requested via read commands directed to the NVMs, forexample if a particular page is present in a particular buffer before aread command for the particular page is to be sent. In some embodimentsand/or usage scenarios, pages other than in response to the commandssent are provided by the NVMs intermixed with the pages provided inresponse to the commands sent, e.g. pages provided in response to readcommands sent for other activities.

In various embodiments, computations for R0 and R1, as illustrated byFIG. 11, are performed at least in part as illustrated by FIGS. 14A and14B. For a first example, read commands for all data pages necessary tocompute corresponding R0 and R1 pages are sent to one or more NVMs asillustrated by FIG. 14A. The pages of data received in response to theread commands are processed as the pages are received to compute the R0and the R1 pages, as illustrated by FIG. 11. For a second example, readcommands for a pair (corresponding, e.g., to two planes of a dual-planeNVM) of R0 and R1 pages are sent to one or more NVMs as illustrated byFIG. 14A. The pages of data received in response to the read commandsare processed as the pages are received to compute the R0 and the R1pages, as illustrated by FIG. 11.

In various embodiments, computations for Pj, as illustrated by FIG. 12,are performed at least in part as illustrated by FIGS. 14A and 14B. Fora first example, read commands for all data pages necessary to compute aparticular Pj page are sent to one or more NVMs as illustrated by FIG.14A. The pages of data received in response to the read commands areprocessed as the pages are received to compute the Pj page, asillustrated by FIG. 12. For a second example, read commands for a pairof Pj pages (corresponding, e.g., to two planes of a dual-plane NVM) aresent to one or more NVMs as illustrated by FIG. 14A, and the pages ofdata received are processed as received, as illustrated by FIG. 14B, tocompute the pair of Pj pages.

In various embodiments, computations related to determining recoveryvalues (such as computations for R0′ and R1′), as illustrated by any ofFIGS. 13A-13D, are performed at least in part as illustrated by FIGS.14A and 14B. For a first example, read commands for all data pagesnecessary to compute a particular R0′ page and a particular R1′ are sentto one or more NVMs as illustrated by FIG. 14A. The pages of datareceived in response to the read commands are processed as the pages arereceived to compute the R0′ and R1′ pages, as illustrated by FIG. 13A.For a second example, read commands for a pair of R0′ and R1′ pages(corresponding, e.g., to two planes of a dual-plane NVM) are sent to oneor more NVMs as illustrated by FIG. 14A, and the pages of data receivedare processed as received, as illustrated by FIG. 14B, to compute thepair of R0′ and R1′ pages.

FIGS. 15A-15C illustrate selected details of an embodiment of backingout of a computation of higher-level redundancy information with respectto a write provided to NVMs, for instance in a context such asassociated with FIG. 11. FIG. 15A illustrates selected details of anembodiment of sending a plurality of write commands to one or more NVMsvia issuing (Issue Write Operation 1502A), checking if all of thecommands have been sent (All Issued?1503A), and if not, then loopingback to send another of the commands. Note that other embodiments arecontemplated where a plurality of commands are issued at a time, ratherthan one at a time.

FIG. 15B illustrates selected details of an embodiment of processingwrite completion and status information received from the NVMs inresponse to the write commands sent as illustrated in FIG. 15A. A checkis made to determine if a write has completed without errors (Write OK?1502B). If so, then a check is made to determine if all writes have beencompleted (Writes Finished? 1504B). If so, then processing is complete(End 1599B). If a write has been completed but with a (lower-level)error such as a program failure, then the flow proceeds to “undo” theeffect of the write with respect to higher-level redundancy informationcomputation (Backout Write from Redundancy 1503B). More specifically,data for the write with the lower-level error is de-computed from anycorresponding higher-level redundancy information computations (assumingthat the data for the write had already been included in thecorresponding higher-level redundancy computations under a presumptionthat the write would succeed). For example, a lower-level write failureis detected on a particular page j. In response, revised R0 and R pagesare computed such that page j data (Pj) is set to zero. FIG. 15Cillustrates selected details of an embodiment of a computation for asingle byte of a revised R0 (nR0) and a single byte of a revised R1(nR1), where j is the page of the lower-level write failure. Note thatin contexts of FIG. 12 such as associated with FIG. 11, if the finitefield is a Galois Field the subtraction operation (“-”) illustrated inFIG. 15C is equivalent to a logical XOR operation. Other processing (notillustrated) is performed, in various embodiments, to store the pagewith the lower-level write failure (Pj), as well as the revisedhigher-level redundancy pages (nR0 and nR1).

Other than reception of write completion and status information inresponse to the commands sent as illustrated in FIG. 15A, the processingillustrated in FIG. 15B is independent of processing illustrated in FIG.15A. In various scenarios, arrival order of the write completion andstatus information varies according to the NVM type, state, operatingenvironment, and other factors, and in some circumstances is differentthan sending order or arrival order of the write commands correspondingto the arriving write completion and status information. As processingof FIG. 15A is independent of FIG. 15B (other than write completion andstatus information arrival being dependent on a corresponding writecommand being sent), in some embodiments and/or usage scenarios, writecommands are being sent (FIG. 15A) while write completion and statusinformation is being received/processed (FIG. 15B).

In some embodiments and/or usage scenarios, a significant latencytranspires between write commands being sent to the NVMs and receptionof write completion and status information from the NVMs in response tothe write commands. In some embodiments and/or usage scenarios, writecompletion and status information other than in response to the commandssent as illustrated in FIG. 15A are provided by the NVMs intermixed withthe write completion and status information provided in response to thecommands sent as illustrated in FIG. 15A, e.g. write completion andstatus information provided in response to write commands sent for otheractivities.

In various embodiments and/or usage scenarios, one or more pages thatwould otherwise be used for data information are unused. In variousscenarios an unused page is a first, middle, or last page of a block.R-block, stripe, or sequence of pages any kind. In some circumstances,unused pages are unused a priori (“left out”), and in some circumstancesunused pages are unused after some use (“removed from service”). Anexample of an unused page that is left out is a page that ismanufactured incorrectly. An example of an unused page that is removedfrom service is a page that fails to write properly (e.g. as describedas a lower-level write error with respect to FIG. 15B). Processing, e.g.relating to FIGS. 10-12, 13A-13D, 14A-14B, and 15A-15B, skips over anyunused pages (whether left out or removed from service), such as byomitting the unused pages entirely from computations, or by performingcomputations as if all data on the unused pages were zero.

Fractional Higher-Level Redundancy

In the foregoing non-fractional RASIE techniques, storage capacityequivalent to an integral number of flash die (out of N total die) isdedicated to higher-level redundancy, enabling recovery from varioustypes of errors. For example, out of 32 flash (e.g. NAND) die, one ofthe die is used for (non-fractional) RASIE-1 (e.g. RAID-5-like)redundancy, reducing capacity by 1/32^(nd), but providing protectionagainst various types of errors.

However, in some embodiments and/or usage scenarios, customers ofstorage systems prefer storage capabilities at various binary capacitypoints (for example 256 GB and GB), and dedicating an entire flash die(or a plurality of entire flash die) to error recovery results inincreased costs. Sometimes the increased costs are more than a linearincrease based on additional flash die. For example, providing a 256 GBstorage capability SSD is implementable using 32 8 GB NAND die total. Ifone of the NAND die is used for (non-fractional) RASIE-1, however, thenonly 31 of the NAND die remain for all other storage (user data plus anysystem data, such as mapping data, used by the SSD). In someimplementations, using 33 NAND die increases cost non-linearly, e.g. anextra placement on a printed-circuit board, and further if the NAND dieare in multi-die packages, such as two, four or eight die per package,then more than one die is used.

At a binary capacity of 256 GB, 256*10̂9 user-accessible bytes areprovided, versus 256*2̂30 physical storage bytes provided by 32 8 GB NANDdie, so about 7.37% of the physical storage bytes are available forother than user-accessible data, such as the system data. Dedicating oneentire NAND die (of the 32 total) to higher-level redundancy consumes1/32 of the physical storage bytes, or about 3.13%, leavingapproximately 7.37%−3.13%=4.24% for the system data. If 4.24% issufficient for the system data, then 32 8 GB NAND die are sufficient toimplement the binary capacity of 256 GB while dedicating one of the dieto higher-level redundancy.

At a binary capacity of 128 GB, implemented with 16 8 GB NAND die anddedicating one of the die to higher-level redundancy, approximately7.37%−6.25%=1.12% of the physical storage bytes are available for systemdata. If 1.12% is insufficient for the system data, then additional NANDdie are used (at additional cost) to implement the binary capacity of GBwhile dedicating one of the die to higher-level redundancy.

In some embodiments and/or usage scenarios, a fractional higher-levelredundancy technique reduces RASIE overhead to less than one entireflash die (e.g. a ‘fraction’ of a flash die) while covering varioustypes of errors, such as errors as described with respect to theforegoing (non-fractional) RASIE-1, RASIE-2, and RASIE-3 techniques. Thefractional higher-level redundancy techniques enable RASIE benefits forlower capacity points while retaining binary capacity. In someembodiments, fractional higher-level redundancy techniques includestriping data across multiple blocks of flash devices (e.g. die).

For example, at a binary capacity of 128 GB, implemented with 16 8 GBNAND die, dedicating one-half of one of the die to higher-levelredundancy consumes 1/32 of the physical storage bytes, or about 3.13%.Thus, approximately 7.37%−3.13%=4.24% remain available for the systemdata. If 4.24% is sufficient for the system data, then 16 8 GB NAND dieare sufficient to implement the binary capacity of 128 GB whilededicating one-half of one of the die to higher-level redundancy.

Recall that a (non-fractional) RASIE-1 mode described elsewhere hereinenables recovery from one error by using storage capacity equivalent toone flash die dedicated to higher-level redundancy information. Invarious embodiments, modes respectively termed (fractional) ‘RASIE-½’and (fractional) ‘RASIE-¼’ enable recovery from one error usingrespective storage capacities equivalent to one-half and one-fourth ofone flash die dedicated to higher-level redundancy information. Forexample, RASIE-½ is used for 256 GB SSD and/or GB SSD implementations.For another example, RASIE-¼ is used for 64 GB SSD implementations. Invarious usage scenarios, RASIE-½ and/or RASIE-¼ provide error protectionfor random failures (of, e.g., a read unit, a page, or a block)equivalent to RASIE-1. For example, in some scenarios, RASIE-½ for 256GB and 128 GB SSDs, and RASIE-¼ for GB SSDs, provide error protection ofrandom failures equivalent to protection provided by RASIE-1 for 512 GBSSDs (implemented with, e.g., 64 NAND flash die). Note that storagecapacity dedicated to higher-level redundancy is not limited to power oftwo fractions (e.g. ½ and ¼ as in RASIE-½ and RASIE-¼, respectively),as, for example, (fractional) ‘RASIE-⅓’ dedicates storage capacityapproximately equal to ⅓ of a flash die to higher-level redundancy.

FIGS. 16A-16C illustrate selected details of an embodiment of fractionalhigher-level redundancy. FIG. 16A serves as a key for FIGS. 16B and 16C.As illustrated by the key information of FIG. 16A, each square in FIGS.16B and 16C represents a particular (dual-plane) block (e.g. Bk−1, Bk−2. . . B1, and B0 for k blocks per die) for a particular die (e.g. Dn−1,Dn−2 . . . D1, and D0 for n die total). FIG. 16A also illustrates aparticular R-block having one block (the j^(th) block) from each of thedie. In FIGS. 16B and 16C, blocks used for higher-level redundancy havea bold underlined font. FIG. 16B illustrates an example non-fractionalRASIE embodiment, RASIE-1. FIG. 16C illustrates an example fractionalRASIE embodiment, RAISE-½.

As described elsewhere herein, (fractional) RASIE-1 enables recoveryfrom one error by using storage capacity equivalent to one flash dicdedicated to higher-level redundancy information. In FIG. 16B, thestorage capacity equivalent to one flash die is illustrated by blockshaving bold underline font text (Dn−1 Bk−1, Dn−1 Bk−2 . . . Dn−1 B1, andDn−1 B0). Thus the higher-level redundancy information is storedentirely in a single dedicated die, die Dn−1. In other embodiments (notillustrated), the higher-level redundancy information for RASIE-1 isstored in a different die (e.g. die Dn−2, blocks Dn−2 Bk−1 . . . Dn−2B0). In yet other embodiments (not illustrated), the higher-levelredundancy information for RASIE-1 is stored in blocks of various die(e.g. blocks Dn−1 Bk−1, Dn−2 Bk−2 . . . D0 B0). In yet other embodiments(not illustrated), the higher-level redundancy information is stored inblocks such that each R-block ‘contributes’ one block, with the onecontributed block being any of the blocks in the R-block. For all of theaforementioned RASIE-1 embodiments, the higher-level redundancyinformation is shared across each R-block, as illustrated by the textbracket “RASIE Shared” bracketing each R-block in the figure.

As described elsewhere herein, (fractional) RASIE-½ enables recoveryfrom one error by using storage capacity equivalent to one-half of oneflash die dedicated to higher-level redundancy information. In FIG. 16C,the storage capacity equivalent to one-half of one flash die isillustrated by blocks having bold underline font text (Dn−1 Bk−1 . . .Dn−1 B3, and Dn−1 B1). Thus the higher-level redundancy information isstored entirely in one-half of a single dedicated die, every other blockof die Dn−1. In other embodiments (not illustrated), the higher-levelredundancy information for RASIE-½ is stored in every other block of dieDn−2 (e.g. blocks Dn−2 Bk−1 . . . Dn−2 B3, and Dn−2 B1). In yet otherembodiments (not illustrated), the higher-level redundancy informationis stored in blocks such that each pair of R-blocks contributes oneblock, with the one contributed block being any of the blocks in theR-block pair. For all of the aforementioned RASIE-½ embodiments, thehigher-level redundancy information is shared across each pair ofR-blocks, as illustrated by the text bracket “RASIE Shared” bracketingeach R-block pair in the figure.

In various embodiments and/or usage scenarios RASIE higher-levelredundancy (e.g. RASIE-1 and RASIE-½) is used for higher-level errorcorrection. When writing pages in each flash (e.g. NAND) die, alower-level error-correcting code (such as a BCH or LDPC code) is usedto protect data within individual pages of the flash die. The RASIEredundancy is an orthogonal, higher-level of redundancy applied across anumber of pages (such as a specified number of pages from each ofrespective different flash die) to enable recovery from various errorconditions. A first example of the various error conditions is a flashpage that is uncorrectable using the lower-level redundancy because theflash page has accumulated too many errors for the lower-levelredundancy to correct. A second example is a failed word line of one ofthe flash die that results in a portion (e.g. a page) of the flash diehaving the failed word line being inaccessible. A third example is afailed block of one of the flash die that results in a data of thefailed block being inaccessible. A fourth example is an entire failedflash die that results in all data of the failed flash die beinginaccessible. In various situations, the second, third, and fourthexamples are physical failure mechanisms that are exemplary of hard(e.g. persistent) errors.

In some embodiments, RASIE (e.g. non-fractional RASIE such as RASIE-1 orfractional RASIE such as RASIE-½) uses an error-correcting code. Inother embodiments, the RASIE redundancy uses an erasure-correcting codesince a location of error(s) is known (e.g. the pages or portionsthereof that failed to be corrected by lower-level redundancy). Forexample, a parity (XOR) code enables correction of one erasure using oneredundant position out of N. RS codes enable correction of erasures, andan RS code using J redundant positions out of N enable correction of Jerasures. Other erasure correcting techniques, such as those describedin elsewhere herein are usable.

In some embodiments, RASIE redundancy information is stored by writingdata in a “striped” fashion (e.g. as illustrated by Striping Direction600 of FIG. 6). One page from each flash (e.g. NAND) die is written in adetermined order, wrapping around to write the next page in each die,until one block of each of the die has been written. E.g., the RASIEredundancy information is stored in a “die first, page second, blockthird” order that fills one block from each die before storing data intoa second block in each die.

Because the aforementioned striping order writes an entire block in eachdie before writing to a second block in each die, block failures aremanaged, in some embodiments, with a full die of redundancy—one die outof N dedicated to storing the RASIE overhead. (Or equivalently, 1/Nth ofthe capacity distributed among the die.)

In various embodiments and/or usage scenarios, however, common forms ofphysical failures are not die failures—full die failures are perhaps1/10th or less as likely as other physical failures (such as block orword line failures).

A problem with using one die out of N (or the equivalent in capacitydistributed among the die) to store RASIE information for recovery ofblock failures is that overhead for the RASIE information is 1/N. In asmall-capacity SSD, where N is small, the overhead becomes a higherpercentage of the capacity, and the overhead plus system data is largerthan the 2̂30/10̂9 factor that is the difference between flash storagecapacity and binary capacity.

The inventor has realized that smaller capacity drives are lesssensitive to die failures than larger capacity drives, as the smallercapacity drives have fewer flash die than the larger capacity drives.The inventor has further realized that a revised striping order isusable to protect against non-die physical failures without usingexcessive overhead. RASIE-½, as illustrated, e.g., by FIG. 16C is anexample of the foregoing.

The revised striping order used for some implementations of fractionalRASIE (e.g. RASIE-½ and RASIE-¼) interleaves writing pages among anumber of blocks in a group of blocks, so that the striping order insome embodiments is “die first, block within group of blocks, page,among groups of blocks.” For example, given a group of K blocks per eachof N die, one page from each of the K blocks is written across all ofthe die (K*N pages total), and one (or more) of the pages contains RASIEhigher-level redundancy information protecting the entire group of K*Npages (that forms one erasure-correcting codeword). Because no more thanone page per block is used in the pages covered by the RASIEhigher-level redundancy information (one of the erasure-correctingcodewords), any single-block failure is still correctable. (Or, withmore than a single-erasure-correcting code, more than a single-blockfailure is still correctable.)

In various embodiments, the pages within the K*N pages that form oneerasure-correcting codeword are written in other orders, or multiple ofthe erasure-correcting codewords are written in an interleaved fashion.In some usage scenarios, a die-first order of writing enables higherperformance.

In some embodiments, the value of K is an integer divisor of the numberof blocks per plane of the flash (or blocks per die of the flash) sothat all blocks within each of the die are used in a same manner. Infurther embodiments where the number of blocks per plane (or blocks perdie) is a power of two or is divisible by a power of two, the value of Kis a power of two.

In various embodiments, the value of K is adjusted based on capacity orother factors. For example, the product K*N is kept constant to maintaina same percentage overhead as a number of die is changed. For anotherexample, the value of K*N is adjusted to achieve a desired degree ofprotection (an amount of data protected by an erasure-correcting code).

In various embodiments, RASIE redundancy being shared is a singleerasure-correcting code (one portion out of N), or alternatively aJ-erasure-correcting code (J portions out of N). Fractional RASIEincreases the value of N to lower the overhead for any value of J. Forexample, by doubling the value of K, the value of J can be doubledwithout increasing the percentage overhead. This is sometimes preferableas, for example, the chance of getting more than two random errors (orerasures) out of 2*N pages is lower than the chance of getting tworandom errors (or erasures) out of just N pages.

In various embodiments, fractional RASIE (e.g. RASIE-½ and RASIE-¼)higher-level redundancy information computation is performed similarlyto non-fractional RASIE (e.g. RASIE-1) higher-level redundancycomputation, except that multiple data blocks within a particular dieare are covered by each block of higher-level redundancy information.See, for example, FIGS. 10-12, and associated description elsewhereherein. In various embodiments, fractional RASIE higher-level redundancyerror recovery is performed similarly to non-fractional RASIEhigher-level redundancy error recovery, except that more data blocks arecovered by each block of higher-level redundancy computation. See, forexample, FIGS. 13A-D, 14A-B, and 15A-C, and associated descriptionelsewhere herein.

Example Implementation Techniques

In some embodiments, various combinations of all or any portions ofoperations performed by a system implementing fractional higher-levelredundancy for NVMs (e.g. flash memories, such as NAND flash memories),a computing-host flash memory controller, and/or an SSD controller (suchas SSD Controller 100 of FIG. 1A), and portions of a processor,microprocessor, system-on-a-chip,application-specific-integrated-circuit, hardware accelerator, or othercircuitry providing all or portions of the aforementioned operations,are specified by a specification compatible with processing by acomputer system. The specification is in accordance with variousdescriptions, such as hardware description languages, circuitdescriptions, netlist descriptions, mask descriptions, or layoutdescriptions. Example descriptions include: Verilog, VHDL, SPICE, SPICEvariants such as PSpice, IBIS, LEF, DEF, GDS-II, OASIS, or otherdescriptions. In various embodiments, the processing includes anycombination of interpretation, compilation, simulation, and synthesis toproduce, to verify, or to specify logic and/or circuitry suitable forinclusion on one or more integrated circuits. Each integrated circuit,according to various embodiments, is designable and/or manufacturableaccording to a variety of techniques. The techniques include aprogrammable technique (such as a field or mask programmable gate arrayintegrated circuit), a semi-custom technique (such as a wholly orpartially cell-based integrated circuit), and a full-custom technique(such as an integrated circuit that is substantially specialized), anycombination thereof, or any other technique compatible with designand/or manufacturing of integrated circuits.

In some embodiments, various combinations of all or portions ofoperations as described by a computer readable medium having a set ofinstructions stored therein, are performed by execution and/orinterpretation of one or more program instructions, by interpretationand/or compiling of one or more source and/or script languagestatements, or by execution of binary instructions produced bycompiling, translating, and/or interpreting information expressed inprogramming and/or scripting language statements. The statements arecompatible with any standard programming or scripting language (such asC, C++, Fortran, Pascal, Ada, Java, VBscript, and Shell). One or more ofthe program instructions, the language statements, or the binaryinstructions, are optionally stored on one or more computer readablestorage medium elements. In various embodiments, some, all, or variousportions of the program instructions are realized as one or morefunctions, routines, sub-routines, in-line routines, procedures, macros,or portions thereof.

CONCLUSION

Certain choices have been made in the description merely for conveniencein preparing the text and drawings, and unless there is an indication tothe contrary, the choices should not be construed per se as conveyingadditional information regarding structure or operation of theembodiments described. Examples of the choices include: the particularorganization or assignment of the designations used for the figurenumbering and the particular organization or assignment of the elementidentifiers (the callouts or numerical designators, e.g.) used toidentify and reference the features and elements of the embodiments.

The words “includes” or “including” are specifically intended to beconstrued as abstractions describing logical sets of open-ended scopeand are not meant to convey physical containment unless explicitlyfollowed by the word “within.”

Although the foregoing embodiments have been described in some detailfor purposes of clarity of description and understanding, the inventionis not limited to the details provided. There are many embodiments ofthe invention. The disclosed embodiments are exemplary and notrestrictive.

It will be understood that many variations in construction, arrangement,and use are possible consistent with the description, and are within thescope of the claims of the issued patent. For example, interconnect andfunction-unit bit-widths, clock speeds, and the type of technology usedare variable according to various embodiments in each component block.The names given to interconnect and logic are merely exemplary, andshould not be construed as limiting the concepts described. The orderand arrangement of flowchart and flow diagram process, action, andfunction elements are variable according to various embodiments. Also,unless specifically stated to the contrary, value ranges specified,maximum and minimum values used, or other particular specifications(such as flash memory technology types; and the number of entries orstages in registers and buffers), are merely those of the describedembodiments, are expected to track improvements and changes inimplementation technology, and should not be construed as limitations.

Functionally equivalent techniques known in the art are employableinstead of those described to implement various components, sub-systems,operations, functions, routines, sub-routines, in-line routines,procedures, macros, or portions thereof. It is also understood that manyfunctional aspects of embodiments are realizable selectively in eitherhardware (e.g., generally dedicated circuitry) or software (e.g., viasome manner of programmed controller or processor), as a function ofembodiment dependent design constraints and technology trends of fasterprocessing (facilitating migration of functions previously in hardwareinto software) and higher integration density (facilitating migration offunctions previously in software into hardware). Specific variations invarious embodiments include, but are not limited to: differences inpartitioning; different form factors and configurations; use ofdifferent operating systems and other system software; use of differentinterface standards, network protocols, or communication links; andother variations to be expected when implementing the concepts describedherein in accordance with the unique engineering and businessconstraints of a particular application.

The embodiments have been described with detail and environmentalcontext well beyond that required for a minimal implementation of manyaspects of the embodiments described. Those of ordinary skill in the artwill recognize that some embodiments omit disclosed components orfeatures without altering the basic cooperation among the remainingelements. It is thus understood that much of the details disclosed arenot required to implement various aspects of the embodiments described.To the extent that the remaining elements are distinguishable from theprior art, components and features that are omitted are not limiting onthe concepts described herein.

All such variations in design are insubstantial changes over theteachings conveyed by the described embodiments. It is also understoodthat the embodiments described herein have broad applicability to othercomputing and networking applications, and are not limited to theparticular application or industry of the described embodiments. Theinvention is thus to be construed as including all possiblemodifications and variations encompassed within the scope of the claimsof the issued patent.

1-22. (canceled)
 23. A method comprising: writing a respective first data storage unit of each of a plurality of non-volatile memory devices, the respective first data storage units comprising a first group of units; writing a respective second data storage unit of each of the plurality of non-volatile memory devices, the respective second data storage units comprising a second group of units, the first group of units and the second group of units comprising a recovery unit; generating redundancy data for protecting data of all data storage units of the recovery unit; storing the redundancy data to an integer number of storage units of the recovery unit, the integer number being less than a number of groups of units in the recovery unit; and recovering data for an unreadable data storage unit of the recovery unit using the redundancy data.
 24. The method of claim 23 further comprising: the plurality of non-volatile memory devices include a plurality of flash die, each flash die including a plurality of blocks, each block including a plurality of pages.
 25. The method of claim 24 further comprising: the data storage units include pages; wherein the method further includes: writing a respective first page to each of a first block of the plurality of flash die; writing a respective second page to each of a second block of the plurality of flash die; and wherein the recovery unit includes one page from each of the first block and the second block from the plurality of flash die.
 26. The method of claim 24 further comprising: the data storage units include blocks; the recovery unit includes a selected number of blocks from each of the plurality of non-volatile memory devices; wherein the selected number includes at least two blocks from each of the plurality of non-volatile memory devices; and the redundancy data is stored to fewer than one block per group of units in the recovery unit.
 27. The method of claim 26 further comprising: the selected number is an integer divisor of a number of blocks per flash die.
 28. The method of claim 26 further comprising: adjusting the selected number of blocks from each of the plurality of non-volatile memory devices to maintain a constant number of blocks in each recovery unit as a number of non-volatile memory devices is changed.
 29. The method of claim 26 further comprising: maintaining a limit on an amount of storage overhead devoted to redundancy data by devoting less than an amount of blocks in a single flash die of the plurality of non-volatile memory devices to storage of redundancy data.
 30. The method of claim 23 further comprising: the integer number being one half the number of groups of units in the recovery unit.
 31. The method of claim 23 further comprising: the recovery unit further comprising a third group of units and a fourth group of units; and the integer number being one quarter the number of groups of units in the recovery unit.
 32. An apparatus comprising: a plurality of non-volatile memory devices including flash die, each flash die including a plurality of blocks, each block including a plurality of pages; a storage controller configured to: write a respective first data storage unit of each of the plurality of non-volatile memory devices, the respective first data storage units comprising a first group of units; write a respective second data storage unit of each of the plurality of non-volatile memory devices, the respective second data storage units comprising a second group of units, the first group of units and the second group of units comprising a recovery unit; generate redundancy data for protecting data of all data storage units of the recovery unit; store the redundancy data to an integer number of storage units of the recovery unit, the integer number being less than a number of groups of units in the recovery unit; and recover data for an unreadable data storage unit of the recovery unit using the redundancy data.
 33. The apparatus of claim 32 further comprising: the data storage units include pages; wherein the storage controller is further configured to: write a respective first page to each of a first block of a plurality of flash die; write a respective second page to each of a second block of the plurality of flash die; and wherein the recovery unit includes one page from each of the first block and the second block from the plurality of flash die.
 34. The apparatus of claim 32 further comprising: the data storage units include blocks; wherein the recovery unit includes at least two blocks from each of the plurality of flash die; and the storage controller is further configured to store the redundancy data to fewer than one block per group of units in the recovery unit.
 35. The apparatus of claim 34 further comprising: the recovery unit includes a selected number of blocks from each of the plurality of non-volatile memory devices.
 36. The apparatus of claim 35 further comprising: the selected number is an integer divisor of a number of blocks per flash die.
 37. The apparatus of claim 35 comprising the storage controller further configured to: adjust the selected number of blocks from each of the plurality of non-volatile memory devices to maintain a constant number of blocks in each recovery unit as a number of non-volatile memory devices is changed.
 38. The apparatus of claim 34 comprising the storage controller further configured to: maintain a limit on an amount of storage overhead devoted to redundancy data by devoting less than an amount of blocks in a single flash die of the plurality of non-volatile memory devices to storage of redundancy data.
 39. An apparatus comprising: a plurality of non-volatile solid state memory die, each die including a plurality of blocks, each block including a plurality of pages, including: a first die of the plurality of non-volatile solid state memory die including respective first block and second block for storing user data; a second die of the plurality of non-volatile solid state memory die including respective first block and second block for storing user data; a third die of the plurality of non-volatile solid state memory die including respective first block for storing redundancy data and respective second block for storing user data; the respective first blocks and second blocks of the first die, the second die, and the third die comprising a recovery unit which shares redundancy data for data recovery; a data storage controller configured to manage storage of data for the plurality of non-volatile solid state memory die, including managing a data recovery operations to recover data from an unreadable page from the recovery unit via utilizing the redundancy data.
 40. The apparatus of claim 39 further comprising: the respective first blocks from the first die, the second die, and the third die comprise a first group of units; and the respective second blocks from the first die, the second die, and the third die comprise a second group of units.
 41. The apparatus of claim 40 further comprising: the recovery unit includes a selected number of blocks from each of the plurality of non-volatile solid state memory die, wherein the selected number includes at least two blocks from each of the plurality of non-volatile solid state memory die; and the data storage controller is further configured to store the redundancy data to fewer than one block per group of units in the recovery unit.
 42. The apparatus of claim 39, comprising the data storage controller further configured to: maintain a limit on an amount of storage overhead devoted to redundancy data by devoting less than the amount of blocks in a single non-volatile solid state memory die of the plurality of non-volatile solid state memory die to storage of redundancy data; and adjust an amount of blocks devoted to storing redundancy data when an amount of available non-volatile solid state memory die changes. 